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Approach to the Diagnosis of Neuroendocrine Lung Neoplasms: Variabilities and Pitfalls
Approach to the Diagnosis of Neuroendocrine Lung Neoplasms: Variabilities and Pitfalls Samuel P. Hammar, MD With the publication of the spectrum of neuroendocrine proliferations and neoplasms and the features and criteria for diagnosing neuroendocrine lung neoplasms, there is more agreement in making a specific pathologic diagnosis of a neuroendocrine lung neoplasm. However, problems exist, especially in diagnosing well-differentiated neuroendocrine carcinomas (atypical carcinoids), large-cell neuroendocrine carcinomas, and even some smallcell lung cancers. Some of this disagreement has to do with a pathologist’s perception of sizes and shapes of cells. Nonneuroendocrine small-cell carcinomas exist and include small-cell squamous cell carcinoma, small cell adenocarcinoma, and basaloid carcinoma. Nonneuroendocrine lung cancers, especially large-cell undifferentiated carcinoma and poorly differentiated adenocarcinoma, not infrequently express neuroendocrine markers immunohistochemically. Semin Thorac Cardiovasc Surg 18:183-190 © 2006 Elsevier Inc. All rights reserved.
W
ith the publication of the spectrum of neuroendocrine proliferations and neoplasms (Table 1), and the features and criteria for diagnosing neuroendocrine lung neoplasms (Tables 2 and 3), there is more agreement in making a specific pathologic diagnosis of a neuroendocrine lung neoplasm.1,2 However, problems exist, especially in diagnosing well-differentiated neuroendocrine carcinomas (atypical carcinoids), large-cell neuroendocrine carcinomas, and even some small-cell lung cancers. Some of this disagreement has to do with a pathologist’s perception of size and shapes of cells. Neuroendocrine lung neoplasms referred to by Warren and coworkers3 as well-differentiated neuroendocrine carcinomas have also been referred to by other names, the current, most frequent being atypical carcinoid.4 Other reports refer to these as malignant carcinoids,5 peripheral small cell carcinoma of lung resembling carcinoid tumor,6 and Kulchitzky cell carcinoma.7 The descriptions of this neoplasm have been fairly similar. In contrast to typical bronchial carcinoids, atypical carcinoids (well-differentiated neuroendocrine carcinomas) occur in the periphery of the lung in more than 60% of cases. They are typically yellow–tan and often well-demarcated and histologically have an organoid or some other type of “carcinoid” appearance. These tumors have higher mitotic activity than typical carcinoids and usually show areas of degeneration and necrosis. From the Diagnostic Specialties Laboratory, Bremerton, Washington. Address reprint requests to Samuel P Hammar, MD, Diagnostic Specialties Laboratory, 700 Lebo Blvd., Bremerton, WA 98310. E-mail: shammar@ harrisonmedical.org
1043-0679/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.semtcvs.2006.08.004
The current criteria for diagnosing this entity are listed in Table 3. Likewise, there has been an evolution in the nosology and understanding of large-cell neuroendocrine carcinoma of the lung. In 1978 Gould and Chejfec8 demonstrated ultrastructurally and biochemically that some tumors diagnosed histologically as large-cell undifferentiated carcinomas represented neuroendocrine carcinomas. This was followed in 1981 by a report by McDowell and coworkers,9 in which they reported seven cases that had been diagnosed as squamous carcinoma, adenocarcinoma, or large-cell undifferentiated carcinoma, whose neoplastic cells contained neuroendocrine granules when examined by electron microscopy and contained serotonin when examined biochemically. Hammond and Sause10 in 1985 reported on eight large-cell neuroendocrine carcinomas, seven of which had been diagnosed histologically as large-cell undifferentiated carcinomas. Their report was followed by that of Neal and coworkers,11 who described 19 neuroendocrine tumors of the lung, which represented 9% of the 247 tumors studied. Four had been diagnosed histologically as poorly differentiated carcinoma; five as poorly differentiated adenocarcinoma; two as undifferentiated non-small-cell, non-large-cell carcinoma; six as largecell undifferentiated carcinoma; and one each as adenocarcinoma and poorly differentiated adenosquamous carcinoma. In 1989, Barbareschi and coworkers12 reported a case of large-cell neuroendocrine carcinoma in the lung of a 70-yearold man who was found on routine chest radiograph to have a “coin” lesion in the left-upper lobe. The neoplasm was extensively necrotic and was initially diagnosed as a large-cell 183
S.P. Hammar
184 Table 1 The Spectrum of Neuroendocrine Proliferations and Neoplasms I. Neuroendocrine cell hyperplasia and tumourlets
II. Tumors with neuroendocrine morphology III. Non-small-cell carcinomas with neuroendocrine differentiation
IV. Other tumors with neuroendocrine properties
A. Neuroendocrine cell hyperplasia (1) Neuroendocrine cell hyperplasia associated with fibrosis and/or inflammation (2) Neuroendocrine cell hyperplasia adjacent to carcinoid tumors (3) Diffuse idiopathic neuroendocrine cell hyperplasia with or without airway fibrosis/obstruction Tumourlets A. Typical carcinoid B. Atypical carcinoid C. Large cell neuroendocrine carcinoma D. Small cell carcinoma A. Pulmonary blastoma B. Primitive neuroectodermal tumor C. Desmoplastic round cell tumor D. Carcinomas with rhabdoid phenotype E. Paraganglioma F. Amphricrine carcinoma G. Primitive neuroectodermal tumor
hilum of the left lung, a 1.5-cm nodule at the left heart border, and right inguinal and axillary masses. The right axillary mass was biopsied and the initial diagnosis was that of a metastatic large-cell undifferentiated carcinoma from the lung. The patient was treated with lomustine at 130 mg/m2 in 6-week cycles for 2 years. The tumor completely disappeared and the patient was free of disease 4 years after diagnosis and treatment. Several weeks after this article appeared in publication, a Letter to the Editor in the Journal of the American Medical Association15 raised concern that the neoplasm reported as a metastatic large-cell undifferentiated lung carcinoma was, in fact, a malignant lymphoma, probably a diffuse “histiocytic” lymphoma. Dr. Vosika, the author of the initial report, sent the biopsy slides of the tumor to three lung tumor pathology experts, who offered their opinion as to the correct histologic diagnosis of the tumor. Dr. Mary Matthews16 opined the neoplasm was a small-cell undifferentiated carcinoma, intermediate type; Dr. Raymond Yesner16 stated “the overall impression is that of an intermediate small-cell carci-
undifferentiated carcinoma. The primary and metastatic tumor showed immunostaining for chromogranin-A, keratin, synaptophysin, and calcitonin. The tumor was described as being composed in part of frequent anaplastic giant cells. In 1991 Travis and coworkers13 stated that, compared with small-cell lung carcinoma, the tumor cells of large-cell neuroendocrine carcinomas were larger and had abundant eosinophilic cytoplasm. These cells typically had high mitotic rates and nucleoli could be identified. These tumors had immunohistochemical features of neuroendocrine differentiation and, by electron microscopy, contained neuroendocrine granules. As perhaps best exemplified when classifying nonHodgkin’s malignant lymphomas, there is often considerable variation in opinion among trained, experienced pathologists as to what is a large cell versus a small cell. With respect to neuroendocrine lung neoplasms, this is best illustrated by a case report published in 1979 by Dr. Gerald Vosika.14 This case concerned a 47-year-old man with a 4-cm mass in the Table 2 General Features of Neuroendocrine Neoplasms of Lung Type of NE* Neoplasm
Relative Frequency
Location in Lung
Carcinoid
Rare
Central
Atypical carcinoid
Uncommon
Large-cell neuroendocrine carcinoma
Uncertain
Peripheral in 60% of cases Midzone or peripheral
Small-cell neuroendocrine carcinoma
Frequent; 20% of common lung neoplasms
*NE, neuroendocrine.
Central
Histology-Cytology
Necrosis
Mitotic Rate
Metastases
Uniform cells; variable patterns Organoid; cellular pleomorphism Large undifferentiated cells; vesicular nuclei with large nucleoli Small ovoid, fusiform, or polygonal cells; nucleoli inconspicuous
None
Low
Uncommon
Common
High
Common
Variable
High
Variable incidence
Common
High
Common
Diagnosis of neuroendocrine lung neoplasms
185
Table 3 Criteria for Diagnosis of Neuroendocrine Tumors Typical carcinoid Atypical carcinoid Large-cell neuroendocrine carcinoma
Small-cell carcinoma
A tumor with carcinoid morphology and less than two mitoses 2 mm2 (10 high power field), lacking necrosis and 0.5 cm or larger A tumor with carcinoid morphology with 2–10 mitoses per 2 mm2 (10 high power field) or necrosis (often punctate) (1) A tumor with a neuroendocrine morphology (organoid nesting, palisading, rosettes, trabeculae) (2) High mitotic rate: 11 or greater per 2 mm2 (10 high power field), median of 70 per 2 mm2 (10 high power field) (3) Necrosis (often large zones) (4) Cytologic features of a non-small-cell lung cancer: large cell size, low nuclear to cytoplasmic ratio, vesicular or fine chromatin, and/or frequent nucleoli. Some tumors have fine nuclear chromatin and lack nucleoli, but qualify as non-small-cell lung carcinoma because of large cell size and abundant cytoplasm (5) Positive immunohistochemical staining for one or more neuroendocrine markers (other than neuron-specific enolase) and/or neuroendocrine granules by electron microscopy (1) Small size (generally less than the diameter of three small resting lymphocytes) (2) Scant cytoplasm (3) Nuclei: finely granular nuclear chromatin, absent or faint nucleoli (4) High mitotic rate (11 or greater per 2 mm2 [10 high power field], median of 80 per 2 mm2 [10 high power field]) (5) Frequent necrosis often in large zones
noma, which is showing some large-cell characteristics—ie, 22/40” (22 refers to intermediate small-cell undifferentiated carcinoma and 40 to large-cell undifferentiated carcinoma). Dr. Juan Rosai16 stated “it is a very undifferentiated tumor and the differential diagnosis is between oat-cell carcinoma and large-cell undifferentiated carcinoma. Although I admit there is room for disagreement, I definitely favor the diagnosis of oat-cell carcinoma because of the architectural pattern and nuclear shape.” This case strongly suggests that even among experienced pathologists, the size of neoplastic cells is to a certain extent “in the eyes of the beholder,” which can cause problems in classifying neuroendocrine lung neoplasms. In the nine cases we17 published in 1989 concerning neuroendocrine lung neoplasms, a considerable difference of opinion occurred in classification, even with the knowledge of the ultrastructural and immunohistochemical features of the tumor cells. Marchevsky and coworkers18 evaluated 5-m hematoxylin and eosin (H&E)-stained sections from 28 surgically resected high-grade pulmonary neuroendocrine carcinomas, including 16 small-cell lung carcinomas and 12 neoplasms diagnosed as large-cell neuroendocrine carcinomas. Morphometry demonstrated a considerable overlap in nuclear size in the high-grade neoplasms. Approximately one-third of the small-cell lung carcinomas exhibited considerable numbers of neoplastic cells that were larger than three normal lymphocytes and 4 of 12 neuroendocrine carcinomas had a predominant number of small cells. The authors concluded the rule that the large-cell lymphocyte size ratio greater than 3 helped distinguish large-cell from small-cell neoplastic cells was confirmed in only 9 of 28 cases. Based on their studies, the authors suggested the use of more generic terminology such as “high-grade neuroendocrine carcinoma”
or “grade 3 neuroendocrine carcinoma” for small-cell lung cancer and large-cell neuroendocrine carcinomas. Travis and coworkers19 attempted to validate the current classification of neuroendocrine lung tumors (typical carcinoid, atypical carcinoid, large-cell neuroendocrine carcinoma, and small-cell lung carcinoma). Forty neuroendocrine lung tumors retrieved from the Armed Forces Institute of Pathology files were evaluated independently by five pulmonary pathologists and were classified as to one of the four entities. The participants were stated to have been provided with a set of tables summarizing the criteria for separation of the four major categories. A consensus diagnosis was achieved in the 40 cases (100%) with a majority agreement in 31 of 40 cases (78%) and unanimous agreement in 22 of 40 cases (55%). Unanimous agreement occurred in seven smallcell lung carcinomas (70%), seven typical carcinoids (58%), four atypical carcinoids (50%) and four large-cell neuroendocrine carcinomas (40%). A majority diagnosis was achieved in 11 of 12 typical carcinoids (92%), 9 of 10 smallcell lung cancers (90%), 6 of 8 atypical carcinoids (75%), and 5 of 10 large-cell neuroendocrine carcinomas (50%). The authors concluded the classification of neuroendocrine lung tumors was most reproducible for typical carcinoids and small-cell lung cancers but was less reproducible for atypical carcinoids (well-differentiated neuroendocrine carcinomas) and large-cell neuroendocrine carcinomas. The authors stated the results indicated a need for more careful definition and application of criteria for typical carcinoids versus atypical carcinoids and small-cell carcinoma versus large-cell neuroendocrine carcinoma. Marchevsky and coworkers18 and Lin and coworkers20 used the proliferative⬎ marker MIB-1 (Ki-67) to determine low-grade versus high-grade neuroendocrine lung carcino-
186
Figure 1 This transbronchial biopsy contained aggregates of somewhat crushed, relatively uniform small cells, the findings considered to be most indicative of small-cell lung cancer.
Figure 2 Immunohistochemical evaluation of the neoplastic cells showed intense cytoplasmic immunostaining for chromogranin-A.
Figure 3 Immunohistochemical evaluation of the neoplastic cells showed moderately intense cytoplasmic immunostaining for synaptophysin.
S.P. Hammar
Figure 4 Ki-67 analysis (proliferative phase marker) showed a proliferative index of less than 15%.
Figure 5 Ultrastructural evaluation of the neoplastic cells showed numerous dense core neuroendocrine granules, the findings most consistent with a typical carcinoid.
Figure 6 The neoplasm is composed of relatively small cells that showed squamous differentiation by immunohistochemistry.
Diagnosis of neuroendocrine lung neoplasms
Figure 7 Immunohistochemical evaluation of the neoplastic cells showed cytoplasmic immunostaining for CK5/6 (A) and nuclear immunostaining for p63 (B).
Figure 8 Ultrastructural evaluation of the neoplastic cells showed a moderate number of well-formed intercellular junctions between the neoplastic cells, the findings being most suggestive of squamous differentiation.
187
Figure 9 Some small-cell lung neoplasms are composed of cells showing glandular differentiation, representing small-cell adenocarcinomas.
Figure 10 Ultrastructurally, the small cancer cell shown in Fig. 9 showed distinct glandular features as seen in this electron micrograph.
Figure 11 An uncommon form of lung cancer composed of small cells is referred to as a basaloid carcinoma and closely resembles neuroendocrine neoplasms histologically.
188 mas. The authors found that all low-grade neuroendocrine lung neoplasms showed MIB-1 immunoreactivity in less than 25% of the neoplastic cells in contrast to high-grade neuroendocrine neoplasms that showed MIB-1 immunoreactivity in greater than 50% of the neoplastic cells. Pelosi and coworkers21 studied bronchial biopsies from seven patients with typical or atypical carcinoid tumors that had been overdiagnosed as small-cell carcinomas based on evaluation of bronchial biopsy specimens. Bronchial biopsy specimens from nine consecutive small-cell carcinomas were used as control cases for histologic and immunohistochemical evaluation using cytokeratin, chromogranin-A, synaptophysin, Ki-67, and Thyroid Transcription Factor-1 (TTF-1). Typical carcinoid lung neoplasms were stated to have presented as either central or peripheral lesions composed of tumor cells that had granular and sometimes coarse nuclear chromatin patterns, high levels of chromogranin-A/synaptophysin immunoreactivity, and low (less than 20%) Ki-67 labeling index. The tumor stroma was stated to contain thinwalled blood vessels. In contrast, small-cell lung cancers were stated to show central tumor location, finely dispersed nuclear chromatin, lower levels of chromogranin-A/synaptophysin, and high (greater than 50%) Ki-67 labeling index. The stroma was stated to have contained thick-walled blood vessels with glomeruloid configuration. The authors concluded that, judging from their studies, there was an overdiagnosis of typical carcinoid neoplasms as small-cell carcinomas in small, crushed bronchial biopsy specimens. This was stated to be a significant worldwide problem. The authors of the Pelosi and coworkers study10 stated that careful examination of H&E-stained sections remained the most important tool for the differential diagnosis with the evaluation of tumor cell proliferative index as the most useful ancillary technique. This author saw three such cases in 2005. The first was a 70-year-old man who was diagnosed as having a small-cell carcinoma by bronchial biopsy (Fig. 1). The tumor cells were relatively uniform, showed some crush artifact and distortion, but in the best preserved areas did not show any mitotic activity. Immunohistochemical evaluation showed intense immunostaining for chromogranin-A (Fig. 2) and synaptophysin (Fig. 3) and showed no immunostaining for TTF-1 (most small-cell lung cancers express TTF-1). The Ki-67 analysis showed a proliferative index of less than approximately 15% (Fig. 4), which strongly indicated the neoplasm was a typical carcinoid and not a small-cell lung cancer. When examined by electron microscopy, the tumor cells contained numerous dense core granules (Fig. 5). This author believes the intensity of the chromogranin-A and synaptophysin reaction and the lack of staining for TTF-1 are additional helpful factors in differentiating typical carcinoid from small-cell lung cancer. As previously eluded to, other lung neoplasms have a smallcell morphology. Small-cell squamous carcinomas (Fig. 6) typically show immunostaining for CK5/6 and p63 (Fig. 7) and, ultrastructurally, usually show a fair number of well-defined intercellular desmosome-type junctions (Fig. 8), which are less frequent in small-cell lung cancers. Small-cell adenocarcinomas (Fig. 9) exist and can cause diagnostic confusion unless evalu-
S.P. Hammar ated by ancillary techniques such as electron microscopy (Fig. 10). The other type of small-cell lung cancer that can result in considerable confusion with a neuroendocrine carcinoma is a basaloid carcinoma (Fig. 11). This was described in detail by Brambilla and coworkers.22 Basaloid carcinomas frequently show histologic/cytologic features of neuroendocrine differentiation, such as organoid, trabecular, or rosette growth pattern, and can easily be confused with small-cell lung cancers. Basaloid carcinomas typically do not express neuroendocrine markers, although can occasionally express neural cell adhesion molecule (CD56) and chromogranin-A. They typically show peripheral palisading and, like small-cell lung cancers, have a high mitotic rate. They frequently show central areas of necrosis like smallcell lung cancers.
Neuroendocrine Differentiation in Non-Small-Cell Lung Cancers Neuroendocrine lung cancers may be derived from epithelial cells that undergo neuroendocrine differentiation. Therefore, it might not be surprising that neuroendocrine differentiation is sometimes observed in non-small-cell lung carcinomas (adenocarcinomas, squamous cell carcinomas, and large-cell undifferentiated carcinomas). Visscher and coworkers23 evaluated frozen, unfixed tissue sections from 56 poorly differentiated non-small-cell primary lung neoplasms with monoclonal antibodies against chromogranin-A, synaptophysin, S100 protein, keratin, vimentin, and neurofilament antigens. Histologically, neuroendocrine features were stated to not be present in these neoplasms. However, immunostains for chromogranin-A or synaptophysin were identified in 5 of 17 (29%) large-cell undifferentiated carcinomas and in 4 of 19 (21%) poorly differentiated adenocarcinomas. Diffuse intense immunostaining was present in two large-cell undifferentiated carcinomas and one poorly differentiated adenocarcinoma for synaptophysin. Vimentin or neurofilament expression was observed in 10 of 17 (59%) large-cell undifferentiated carcinomas, 10 of 19 (53%) poorly differentiated adenocarcinomas, and additional neuroendocrine markers in 8 of 9 (89%) cases. Synaptophysin was found in only 1 of 20 (5%) poorly differentiated squamous cell carcinomas. Vimentin was observed in 2 of 20 (10%) squamous cell carcinomas. The authors concluded that immunohistologic evidence of neuroendocrine differentiation was present in a significant number of large-cell undifferentiated carcinomas and poorly differentiated adenocarcinomas and was rare in poorly differentiated squamous cell carcinomas. They also concluded that neuroendocrine differentiation was often accompanied by heterogeneous intermediate filament expression and that neuroendocrine differentiation was not necessarily reflected in the histologic features of the tumor. Linnoila and coworkers24 evaluated paraffin-embedded sections from 113 surgically resected primary lung neoplasms with antibodies against chromogranin-A, Leu7, neuron-specific enolase, serotonin, bombesin, calcitonin, adrenocorticotropic hormone, vasopressin, neurotensin, carcinoembryonic antigen, keratin, vimentin, and neurofila-
Diagnosis of neuroendocrine lung neoplasms ment. They found the majority of carcinoids and small-cell lung carcinomas expressed multiple neuroendocrine markers in a high percentage of tumor cells and that about 50% of non-small-cell lung carcinomas contained subpopulations of tumor cells expressing neuroendocrine markers. They also found that occasional non-small-cell lung carcinomas showed an immunostaining pattern indistinguishable from small-cell lung carcinomas and that neuroendocrine markers were more commonly expressed in large-cell undifferentiated carcinomas and adenocarcinomas than in squamous cell carcinomas. Loy and coworkers25 evaluated 66 neoplasms that had been examined by electron microscopy with a battery of neuroendocrine markers, including neuron-specific enolase, chromogranin-A, Leu7, synaptophysin, and B72.3. Four of 10 squamous carcinomas, 3 of 26 adenocarcinomas, and 1 of 11 large-cell undifferentiated carcinomas showed immunostaining for Leu7. Six of 10 squamous carcinomas, 15 of 26 adenocarcinomas, and 7 of 11 large-cell undifferentiated carcinomas showed immunostaining for neuron-specific enolase. Six of 10 squamous carcinomas, 16 of 26 adenocarcinomas, and 7 of 11 large-cell undifferentiated carcinomas showed immunostaining for synaptophysin. Overall, 34 of 47 (79%) carcinomas without histologic neuroendocrine features expressed at least one neuroendocrine immunohistochemical marker. Nineteen of 19 (100%) neuroendocrine carcinomas were stated to have expressed at least one neuroendocrine marker. Schleusener and coworkers26 evaluated 107 patients with stage IIIA, stage IIIB, and stage IV non-small-cell lung carcinomas (62 adenocarcinomas, 22 squamous cell carcinomas, 18 large-cell undifferentiated carcinomas, and 5 adenosquamous carcinomas) immunohistochemically with antibodies against keratin, synaptophysin, Leu7, and chromogranin-A. Keratin was used as a control and was stated to have been positive in 99.1% of cases. Thirty-five percent of adenocarcinomas, 41% of squamous carcinomas, and 33% of large-cell undifferentiated carcinomas expressed at least one neuroendocrine marker. Somewhat surprising was the finding that there was an increased survival in patients whose tumors expressed one or more neuroendocrine markers, although the authors stated there was no correlation between neuroendocrine markers and response to chemotherapy. The bottom line for pathologists and clinicians is that some neuroendocrine lung cancers are difficult to classify, especially with respect to the categories of well-differentiated neuroendocrine carcinomas (atypical carcinoids) and largecell neuroendocrine carcinomas. Some have advocated a grading system of 1, 2, and 3 for low-grade, intermediategrade, and high-grade neuroendocrine neoplasms, respectively. Others, such as Travis, favor the classification of typical carcinoid, atypical carcinoid, large-cell neuroendocrine carcinoma, and small-cell lung cancer, even though confusion exists in diagnosing atypical carcinoids, large-cell neuroendocrine carcinomas, and even small-cell carcinomas. Clinicians and pathologists should recognize there are neoplasms that show squamous and glandular differentiation composed of relatively small cells that can cause confusion
189 with neuroendocrine neoplasms, usually small-cell lung cancer. Basaloid carcinomas can frequently be misinterpreted as a neuroendocrine carcinoma. Finally, nonneuroendocrine neoplasms, specifically adenocarcinomas, squamous cell carcinomas, and large-cell undifferentiated carcinomas may express neuroendocrine markers by immunohistochemistry. The effect, if any, the morphologic and immunohistochemical features have on treatment of some neuroendocrine lung neoplasms has yet to be completely determined.
References 1. Travis WD, Colby TV, Corrin B, et al: Histological typing of lung and pleural tumors. In collaboration with L.H. Sobin and pathologists from 14 countries. World Health Organization International Classification of Tumours (ed 3). Berlin, Heidelberg, New York, Springer-Verlag, 1999 2. Travis WD, Brambilla E, Muller-Hermelink HG, et al (eds): Pathology and Genetics: Tumours of the Lung, Pleura, Thymus and Heart. Lyon, IARC Press, 2004 3. Warren WH, Memoli VA, Gould VE: Immunohistochemical and ultrastructural analysis of bronchopulmonary neuroendocrine neoplasms. II. Well-differentiated neuroendocrine carcinomas. Ultrastruct Pathol 7:185-199, 1984 4. Arrigoni MG, Woolner LB, Bernatz PE: Atypical carcinoid tumors of the lung. J Thorac Cardiovasc Surg 64:413-1, 1972 5. Leschke H: ¨Uber nur regiona¨r bo¨sartige and u¨ber krebsig entartete Bronchusadenome bzw. Carcinoide Arch Path Anat 328:635-7, 1956 6. Mark EJ, Ramirez JF: Peripheral small cell carcinoma of the lung resembling carcinoid tumor: a clinical and pathologic study of 14 cases. Arch Pathol Lab Med 109:263-269, 1985 7. Paladugu RR, Benfield JR, Pak HY, et al: Bronchopulmonary kulchitzky cell carcinomas. Cancer 55:1303-1311, 1985 8. Gould VE, Chejfec G: Ultrastructural and biochemical analysis of pulmonary “undifferentiated” carcinomas. Hum Pathol 9:377-384, 1978 9. McDowell EM, Wilson TS, Trump BF: Atypical endocrine tumors of the lung. Arch Pathol Lab Med 105:20-28, 1981 10. Hammond ME, Sause WT: Large cell neuroendocrine tumors of the lung: clinical significance and histopathologic definition. Cancer 56: 1624-1629, 1985 11. Neal MH, Kosinki R, Cohen P, Orenstein JM: Atypical endocrine tumors of the lung: a histologic, ultrastructural and clinical study of 19 cases. Hum Pathol 17:1264-1277, 1986 12. Barbareschi M, Mariscotti C, Barberis M, et al: Large cell neuroendocrine carcinoma of the lung. Tumori 75:583-588, 1989 13. Travis WD, Linnoila I, Tsokos MG, et al: Neuroendocrine tumors of the lung with proposed criteria for large cell neuroendocrine carcinoma: an ultrastructural, immunohistochemical and flow cytometric study of 35 cases. Am J Surg Pathol 15:529-533, 1991 14. Vosika GJ: Large cell bronchogenic carcinoma: prolonged disease-free survival following chemotherapy. JAMA 241:594-5, 1979 15. Gibbs FA: Lymphoma versus carcinoma. JAMA 242:514, 1979 16. Vosika GJ: Large cell-small cell bronchogenic carcinoma. JAMA 242: 1259-1260, 1979 17. Hammar S, Bockus D, Remington F, et al: The unusual spectrum of neuroendocrine lung neoplasms. Ultra Pathol 13:515-560, 1989 18. Marchevsky AM, Gal AA, Shah S, et al: Morphometry confirms the presence of considerable nuclear size overlap between “small cells” and “large cells” in high-grade pulmonary neuroendocrine neoplasms. Am J Clin Pathol 116:466-472, 2001 19. Travis WD, Gal AA, Colby TV, et al: Reproducibility of neuroendocrine lung tumor classification. Hum Pathol 29:272-279, 1998 20. Lin O, Olgac S, Green I, et al: Immunohistochemical staining of cytologic smears with MIB-1 helps distinguish low-grade from highgrade neuroendocrine neoplasms. Am J Clin Pathol 120:209-216, 2003 21. Pelosi G, Rodriguez J, Viale G, et al: Typical and atypical carcinoid tumor overdiagnosed as small carcinoma on biopsy specimens: a major
190 pitfall in the management of lung cancer patients. Am J Surg Pathol 29:179-187, 2005 22. Brambilla E: Basaloid carcinoma of the lung, in Corrin B (ed): Pathology of Lung Tumors. New York, NY, Churchill-Livingstone, 1997, pp 71-82 23. Visscher DW, Zarbo RJ, Trojanowski JQ, et al: Neuroendocrine differentiation in poorly-differentiated lung carcinomas: a light microscopic and immunohistologic study. Mod Pathol 3:508-512, 1990 24. Linnoila RI, Mulshine JL, Steinberg SM, et al: Neuroendocrine differ-
S.P. Hammar entiation in endocrine and nonendocrine lung carcinomas. Am J Clin Pathol 90:641-652, 1988 25. Loy TS, Darkow GVD, Quesenberry JT: Immunostaining in the diagnosis of pulmonary neuroendocrine carcinomas: an immunohistochemical study with ultrastructural correlations. Am J Surg Pathol 19: 173-182, 1995 26. Schleusener JT, Tazelaar HD, Jung S, et al: Neuroendocrine differentiation is an independent prognostic factor in chemotherapy-treated non-small cell lung carcinoma. Cancer 77:1284-1291, 1995
W
ith the publication of the spectrum of neuroendocrine proliferations and neoplasms (Table 1), and the features and criteria for diagnosing neuroendocrine lung neoplasms (Tables 2 and 3), there is more agreement in making a specific pathologic diagnosis of a neuroendocrine lung neoplasm.1,2 However, problems exist, especially in diagnosing well-differentiated neuroendocrine carcinomas (atypical carcinoids), large-cell neuroendocrine carcinomas, and even some small-cell lung cancers. Some of this disagreement has to do with a pathologist’s perception of size and shapes of cells. Neuroendocrine lung neoplasms referred to by Warren and coworkers3 as well-differentiated neuroendocrine carcinomas have also been referred to by other names, the current, most frequent being atypical carcinoid.4 Other reports refer to these as malignant carcinoids,5 peripheral small cell carcinoma of lung resembling carcinoid tumor,6 and Kulchitzky cell carcinoma.7 The descriptions of this neoplasm have been fairly similar. In contrast to typical bronchial carcinoids, atypical carcinoids (well-differentiated neuroendocrine carcinomas) occur in the periphery of the lung in more than 60% of cases. They are typically yellow–tan and often well-demarcated and histologically have an organoid or some other type of “carcinoid” appearance. These tumors have higher mitotic activity than typical carcinoids and usually show areas of degeneration and necrosis. From the Diagnostic Specialties Laboratory, Bremerton, Washington. Address reprint requests to Samuel P Hammar, MD, Diagnostic Specialties Laboratory, 700 Lebo Blvd., Bremerton, WA 98310. E-mail: shammar@ harrisonmedical.org
1043-0679/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.semtcvs.2006.08.004
The current criteria for diagnosing this entity are listed in Table 3. Likewise, there has been an evolution in the nosology and understanding of large-cell neuroendocrine carcinoma of the lung. In 1978 Gould and Chejfec8 demonstrated ultrastructurally and biochemically that some tumors diagnosed histologically as large-cell undifferentiated carcinomas represented neuroendocrine carcinomas. This was followed in 1981 by a report by McDowell and coworkers,9 in which they reported seven cases that had been diagnosed as squamous carcinoma, adenocarcinoma, or large-cell undifferentiated carcinoma, whose neoplastic cells contained neuroendocrine granules when examined by electron microscopy and contained serotonin when examined biochemically. Hammond and Sause10 in 1985 reported on eight large-cell neuroendocrine carcinomas, seven of which had been diagnosed histologically as large-cell undifferentiated carcinomas. Their report was followed by that of Neal and coworkers,11 who described 19 neuroendocrine tumors of the lung, which represented 9% of the 247 tumors studied. Four had been diagnosed histologically as poorly differentiated carcinoma; five as poorly differentiated adenocarcinoma; two as undifferentiated non-small-cell, non-large-cell carcinoma; six as largecell undifferentiated carcinoma; and one each as adenocarcinoma and poorly differentiated adenosquamous carcinoma. In 1989, Barbareschi and coworkers12 reported a case of large-cell neuroendocrine carcinoma in the lung of a 70-yearold man who was found on routine chest radiograph to have a “coin” lesion in the left-upper lobe. The neoplasm was extensively necrotic and was initially diagnosed as a large-cell 183
S.P. Hammar
184 Table 1 The Spectrum of Neuroendocrine Proliferations and Neoplasms I. Neuroendocrine cell hyperplasia and tumourlets
II. Tumors with neuroendocrine morphology III. Non-small-cell carcinomas with neuroendocrine differentiation
IV. Other tumors with neuroendocrine properties
A. Neuroendocrine cell hyperplasia (1) Neuroendocrine cell hyperplasia associated with fibrosis and/or inflammation (2) Neuroendocrine cell hyperplasia adjacent to carcinoid tumors (3) Diffuse idiopathic neuroendocrine cell hyperplasia with or without airway fibrosis/obstruction Tumourlets A. Typical carcinoid B. Atypical carcinoid C. Large cell neuroendocrine carcinoma D. Small cell carcinoma A. Pulmonary blastoma B. Primitive neuroectodermal tumor C. Desmoplastic round cell tumor D. Carcinomas with rhabdoid phenotype E. Paraganglioma F. Amphricrine carcinoma G. Primitive neuroectodermal tumor
hilum of the left lung, a 1.5-cm nodule at the left heart border, and right inguinal and axillary masses. The right axillary mass was biopsied and the initial diagnosis was that of a metastatic large-cell undifferentiated carcinoma from the lung. The patient was treated with lomustine at 130 mg/m2 in 6-week cycles for 2 years. The tumor completely disappeared and the patient was free of disease 4 years after diagnosis and treatment. Several weeks after this article appeared in publication, a Letter to the Editor in the Journal of the American Medical Association15 raised concern that the neoplasm reported as a metastatic large-cell undifferentiated lung carcinoma was, in fact, a malignant lymphoma, probably a diffuse “histiocytic” lymphoma. Dr. Vosika, the author of the initial report, sent the biopsy slides of the tumor to three lung tumor pathology experts, who offered their opinion as to the correct histologic diagnosis of the tumor. Dr. Mary Matthews16 opined the neoplasm was a small-cell undifferentiated carcinoma, intermediate type; Dr. Raymond Yesner16 stated “the overall impression is that of an intermediate small-cell carci-
undifferentiated carcinoma. The primary and metastatic tumor showed immunostaining for chromogranin-A, keratin, synaptophysin, and calcitonin. The tumor was described as being composed in part of frequent anaplastic giant cells. In 1991 Travis and coworkers13 stated that, compared with small-cell lung carcinoma, the tumor cells of large-cell neuroendocrine carcinomas were larger and had abundant eosinophilic cytoplasm. These cells typically had high mitotic rates and nucleoli could be identified. These tumors had immunohistochemical features of neuroendocrine differentiation and, by electron microscopy, contained neuroendocrine granules. As perhaps best exemplified when classifying nonHodgkin’s malignant lymphomas, there is often considerable variation in opinion among trained, experienced pathologists as to what is a large cell versus a small cell. With respect to neuroendocrine lung neoplasms, this is best illustrated by a case report published in 1979 by Dr. Gerald Vosika.14 This case concerned a 47-year-old man with a 4-cm mass in the Table 2 General Features of Neuroendocrine Neoplasms of Lung Type of NE* Neoplasm
Relative Frequency
Location in Lung
Carcinoid
Rare
Central
Atypical carcinoid
Uncommon
Large-cell neuroendocrine carcinoma
Uncertain
Peripheral in 60% of cases Midzone or peripheral
Small-cell neuroendocrine carcinoma
Frequent; 20% of common lung neoplasms
*NE, neuroendocrine.
Central
Histology-Cytology
Necrosis
Mitotic Rate
Metastases
Uniform cells; variable patterns Organoid; cellular pleomorphism Large undifferentiated cells; vesicular nuclei with large nucleoli Small ovoid, fusiform, or polygonal cells; nucleoli inconspicuous
None
Low
Uncommon
Common
High
Common
Variable
High
Variable incidence
Common
High
Common
Diagnosis of neuroendocrine lung neoplasms
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Table 3 Criteria for Diagnosis of Neuroendocrine Tumors Typical carcinoid Atypical carcinoid Large-cell neuroendocrine carcinoma
Small-cell carcinoma
A tumor with carcinoid morphology and less than two mitoses 2 mm2 (10 high power field), lacking necrosis and 0.5 cm or larger A tumor with carcinoid morphology with 2–10 mitoses per 2 mm2 (10 high power field) or necrosis (often punctate) (1) A tumor with a neuroendocrine morphology (organoid nesting, palisading, rosettes, trabeculae) (2) High mitotic rate: 11 or greater per 2 mm2 (10 high power field), median of 70 per 2 mm2 (10 high power field) (3) Necrosis (often large zones) (4) Cytologic features of a non-small-cell lung cancer: large cell size, low nuclear to cytoplasmic ratio, vesicular or fine chromatin, and/or frequent nucleoli. Some tumors have fine nuclear chromatin and lack nucleoli, but qualify as non-small-cell lung carcinoma because of large cell size and abundant cytoplasm (5) Positive immunohistochemical staining for one or more neuroendocrine markers (other than neuron-specific enolase) and/or neuroendocrine granules by electron microscopy (1) Small size (generally less than the diameter of three small resting lymphocytes) (2) Scant cytoplasm (3) Nuclei: finely granular nuclear chromatin, absent or faint nucleoli (4) High mitotic rate (11 or greater per 2 mm2 [10 high power field], median of 80 per 2 mm2 [10 high power field]) (5) Frequent necrosis often in large zones
noma, which is showing some large-cell characteristics—ie, 22/40” (22 refers to intermediate small-cell undifferentiated carcinoma and 40 to large-cell undifferentiated carcinoma). Dr. Juan Rosai16 stated “it is a very undifferentiated tumor and the differential diagnosis is between oat-cell carcinoma and large-cell undifferentiated carcinoma. Although I admit there is room for disagreement, I definitely favor the diagnosis of oat-cell carcinoma because of the architectural pattern and nuclear shape.” This case strongly suggests that even among experienced pathologists, the size of neoplastic cells is to a certain extent “in the eyes of the beholder,” which can cause problems in classifying neuroendocrine lung neoplasms. In the nine cases we17 published in 1989 concerning neuroendocrine lung neoplasms, a considerable difference of opinion occurred in classification, even with the knowledge of the ultrastructural and immunohistochemical features of the tumor cells. Marchevsky and coworkers18 evaluated 5-m hematoxylin and eosin (H&E)-stained sections from 28 surgically resected high-grade pulmonary neuroendocrine carcinomas, including 16 small-cell lung carcinomas and 12 neoplasms diagnosed as large-cell neuroendocrine carcinomas. Morphometry demonstrated a considerable overlap in nuclear size in the high-grade neoplasms. Approximately one-third of the small-cell lung carcinomas exhibited considerable numbers of neoplastic cells that were larger than three normal lymphocytes and 4 of 12 neuroendocrine carcinomas had a predominant number of small cells. The authors concluded the rule that the large-cell lymphocyte size ratio greater than 3 helped distinguish large-cell from small-cell neoplastic cells was confirmed in only 9 of 28 cases. Based on their studies, the authors suggested the use of more generic terminology such as “high-grade neuroendocrine carcinoma”
or “grade 3 neuroendocrine carcinoma” for small-cell lung cancer and large-cell neuroendocrine carcinomas. Travis and coworkers19 attempted to validate the current classification of neuroendocrine lung tumors (typical carcinoid, atypical carcinoid, large-cell neuroendocrine carcinoma, and small-cell lung carcinoma). Forty neuroendocrine lung tumors retrieved from the Armed Forces Institute of Pathology files were evaluated independently by five pulmonary pathologists and were classified as to one of the four entities. The participants were stated to have been provided with a set of tables summarizing the criteria for separation of the four major categories. A consensus diagnosis was achieved in the 40 cases (100%) with a majority agreement in 31 of 40 cases (78%) and unanimous agreement in 22 of 40 cases (55%). Unanimous agreement occurred in seven smallcell lung carcinomas (70%), seven typical carcinoids (58%), four atypical carcinoids (50%) and four large-cell neuroendocrine carcinomas (40%). A majority diagnosis was achieved in 11 of 12 typical carcinoids (92%), 9 of 10 smallcell lung cancers (90%), 6 of 8 atypical carcinoids (75%), and 5 of 10 large-cell neuroendocrine carcinomas (50%). The authors concluded the classification of neuroendocrine lung tumors was most reproducible for typical carcinoids and small-cell lung cancers but was less reproducible for atypical carcinoids (well-differentiated neuroendocrine carcinomas) and large-cell neuroendocrine carcinomas. The authors stated the results indicated a need for more careful definition and application of criteria for typical carcinoids versus atypical carcinoids and small-cell carcinoma versus large-cell neuroendocrine carcinoma. Marchevsky and coworkers18 and Lin and coworkers20 used the proliferative⬎ marker MIB-1 (Ki-67) to determine low-grade versus high-grade neuroendocrine lung carcino-
186
Figure 1 This transbronchial biopsy contained aggregates of somewhat crushed, relatively uniform small cells, the findings considered to be most indicative of small-cell lung cancer.
Figure 2 Immunohistochemical evaluation of the neoplastic cells showed intense cytoplasmic immunostaining for chromogranin-A.
Figure 3 Immunohistochemical evaluation of the neoplastic cells showed moderately intense cytoplasmic immunostaining for synaptophysin.
S.P. Hammar
Figure 4 Ki-67 analysis (proliferative phase marker) showed a proliferative index of less than 15%.
Figure 5 Ultrastructural evaluation of the neoplastic cells showed numerous dense core neuroendocrine granules, the findings most consistent with a typical carcinoid.
Figure 6 The neoplasm is composed of relatively small cells that showed squamous differentiation by immunohistochemistry.
Diagnosis of neuroendocrine lung neoplasms
Figure 7 Immunohistochemical evaluation of the neoplastic cells showed cytoplasmic immunostaining for CK5/6 (A) and nuclear immunostaining for p63 (B).
Figure 8 Ultrastructural evaluation of the neoplastic cells showed a moderate number of well-formed intercellular junctions between the neoplastic cells, the findings being most suggestive of squamous differentiation.
187
Figure 9 Some small-cell lung neoplasms are composed of cells showing glandular differentiation, representing small-cell adenocarcinomas.
Figure 10 Ultrastructurally, the small cancer cell shown in Fig. 9 showed distinct glandular features as seen in this electron micrograph.
Figure 11 An uncommon form of lung cancer composed of small cells is referred to as a basaloid carcinoma and closely resembles neuroendocrine neoplasms histologically.
188 mas. The authors found that all low-grade neuroendocrine lung neoplasms showed MIB-1 immunoreactivity in less than 25% of the neoplastic cells in contrast to high-grade neuroendocrine neoplasms that showed MIB-1 immunoreactivity in greater than 50% of the neoplastic cells. Pelosi and coworkers21 studied bronchial biopsies from seven patients with typical or atypical carcinoid tumors that had been overdiagnosed as small-cell carcinomas based on evaluation of bronchial biopsy specimens. Bronchial biopsy specimens from nine consecutive small-cell carcinomas were used as control cases for histologic and immunohistochemical evaluation using cytokeratin, chromogranin-A, synaptophysin, Ki-67, and Thyroid Transcription Factor-1 (TTF-1). Typical carcinoid lung neoplasms were stated to have presented as either central or peripheral lesions composed of tumor cells that had granular and sometimes coarse nuclear chromatin patterns, high levels of chromogranin-A/synaptophysin immunoreactivity, and low (less than 20%) Ki-67 labeling index. The tumor stroma was stated to contain thinwalled blood vessels. In contrast, small-cell lung cancers were stated to show central tumor location, finely dispersed nuclear chromatin, lower levels of chromogranin-A/synaptophysin, and high (greater than 50%) Ki-67 labeling index. The stroma was stated to have contained thick-walled blood vessels with glomeruloid configuration. The authors concluded that, judging from their studies, there was an overdiagnosis of typical carcinoid neoplasms as small-cell carcinomas in small, crushed bronchial biopsy specimens. This was stated to be a significant worldwide problem. The authors of the Pelosi and coworkers study10 stated that careful examination of H&E-stained sections remained the most important tool for the differential diagnosis with the evaluation of tumor cell proliferative index as the most useful ancillary technique. This author saw three such cases in 2005. The first was a 70-year-old man who was diagnosed as having a small-cell carcinoma by bronchial biopsy (Fig. 1). The tumor cells were relatively uniform, showed some crush artifact and distortion, but in the best preserved areas did not show any mitotic activity. Immunohistochemical evaluation showed intense immunostaining for chromogranin-A (Fig. 2) and synaptophysin (Fig. 3) and showed no immunostaining for TTF-1 (most small-cell lung cancers express TTF-1). The Ki-67 analysis showed a proliferative index of less than approximately 15% (Fig. 4), which strongly indicated the neoplasm was a typical carcinoid and not a small-cell lung cancer. When examined by electron microscopy, the tumor cells contained numerous dense core granules (Fig. 5). This author believes the intensity of the chromogranin-A and synaptophysin reaction and the lack of staining for TTF-1 are additional helpful factors in differentiating typical carcinoid from small-cell lung cancer. As previously eluded to, other lung neoplasms have a smallcell morphology. Small-cell squamous carcinomas (Fig. 6) typically show immunostaining for CK5/6 and p63 (Fig. 7) and, ultrastructurally, usually show a fair number of well-defined intercellular desmosome-type junctions (Fig. 8), which are less frequent in small-cell lung cancers. Small-cell adenocarcinomas (Fig. 9) exist and can cause diagnostic confusion unless evalu-
S.P. Hammar ated by ancillary techniques such as electron microscopy (Fig. 10). The other type of small-cell lung cancer that can result in considerable confusion with a neuroendocrine carcinoma is a basaloid carcinoma (Fig. 11). This was described in detail by Brambilla and coworkers.22 Basaloid carcinomas frequently show histologic/cytologic features of neuroendocrine differentiation, such as organoid, trabecular, or rosette growth pattern, and can easily be confused with small-cell lung cancers. Basaloid carcinomas typically do not express neuroendocrine markers, although can occasionally express neural cell adhesion molecule (CD56) and chromogranin-A. They typically show peripheral palisading and, like small-cell lung cancers, have a high mitotic rate. They frequently show central areas of necrosis like smallcell lung cancers.
Neuroendocrine Differentiation in Non-Small-Cell Lung Cancers Neuroendocrine lung cancers may be derived from epithelial cells that undergo neuroendocrine differentiation. Therefore, it might not be surprising that neuroendocrine differentiation is sometimes observed in non-small-cell lung carcinomas (adenocarcinomas, squamous cell carcinomas, and large-cell undifferentiated carcinomas). Visscher and coworkers23 evaluated frozen, unfixed tissue sections from 56 poorly differentiated non-small-cell primary lung neoplasms with monoclonal antibodies against chromogranin-A, synaptophysin, S100 protein, keratin, vimentin, and neurofilament antigens. Histologically, neuroendocrine features were stated to not be present in these neoplasms. However, immunostains for chromogranin-A or synaptophysin were identified in 5 of 17 (29%) large-cell undifferentiated carcinomas and in 4 of 19 (21%) poorly differentiated adenocarcinomas. Diffuse intense immunostaining was present in two large-cell undifferentiated carcinomas and one poorly differentiated adenocarcinoma for synaptophysin. Vimentin or neurofilament expression was observed in 10 of 17 (59%) large-cell undifferentiated carcinomas, 10 of 19 (53%) poorly differentiated adenocarcinomas, and additional neuroendocrine markers in 8 of 9 (89%) cases. Synaptophysin was found in only 1 of 20 (5%) poorly differentiated squamous cell carcinomas. Vimentin was observed in 2 of 20 (10%) squamous cell carcinomas. The authors concluded that immunohistologic evidence of neuroendocrine differentiation was present in a significant number of large-cell undifferentiated carcinomas and poorly differentiated adenocarcinomas and was rare in poorly differentiated squamous cell carcinomas. They also concluded that neuroendocrine differentiation was often accompanied by heterogeneous intermediate filament expression and that neuroendocrine differentiation was not necessarily reflected in the histologic features of the tumor. Linnoila and coworkers24 evaluated paraffin-embedded sections from 113 surgically resected primary lung neoplasms with antibodies against chromogranin-A, Leu7, neuron-specific enolase, serotonin, bombesin, calcitonin, adrenocorticotropic hormone, vasopressin, neurotensin, carcinoembryonic antigen, keratin, vimentin, and neurofila-
Diagnosis of neuroendocrine lung neoplasms ment. They found the majority of carcinoids and small-cell lung carcinomas expressed multiple neuroendocrine markers in a high percentage of tumor cells and that about 50% of non-small-cell lung carcinomas contained subpopulations of tumor cells expressing neuroendocrine markers. They also found that occasional non-small-cell lung carcinomas showed an immunostaining pattern indistinguishable from small-cell lung carcinomas and that neuroendocrine markers were more commonly expressed in large-cell undifferentiated carcinomas and adenocarcinomas than in squamous cell carcinomas. Loy and coworkers25 evaluated 66 neoplasms that had been examined by electron microscopy with a battery of neuroendocrine markers, including neuron-specific enolase, chromogranin-A, Leu7, synaptophysin, and B72.3. Four of 10 squamous carcinomas, 3 of 26 adenocarcinomas, and 1 of 11 large-cell undifferentiated carcinomas showed immunostaining for Leu7. Six of 10 squamous carcinomas, 15 of 26 adenocarcinomas, and 7 of 11 large-cell undifferentiated carcinomas showed immunostaining for neuron-specific enolase. Six of 10 squamous carcinomas, 16 of 26 adenocarcinomas, and 7 of 11 large-cell undifferentiated carcinomas showed immunostaining for synaptophysin. Overall, 34 of 47 (79%) carcinomas without histologic neuroendocrine features expressed at least one neuroendocrine immunohistochemical marker. Nineteen of 19 (100%) neuroendocrine carcinomas were stated to have expressed at least one neuroendocrine marker. Schleusener and coworkers26 evaluated 107 patients with stage IIIA, stage IIIB, and stage IV non-small-cell lung carcinomas (62 adenocarcinomas, 22 squamous cell carcinomas, 18 large-cell undifferentiated carcinomas, and 5 adenosquamous carcinomas) immunohistochemically with antibodies against keratin, synaptophysin, Leu7, and chromogranin-A. Keratin was used as a control and was stated to have been positive in 99.1% of cases. Thirty-five percent of adenocarcinomas, 41% of squamous carcinomas, and 33% of large-cell undifferentiated carcinomas expressed at least one neuroendocrine marker. Somewhat surprising was the finding that there was an increased survival in patients whose tumors expressed one or more neuroendocrine markers, although the authors stated there was no correlation between neuroendocrine markers and response to chemotherapy. The bottom line for pathologists and clinicians is that some neuroendocrine lung cancers are difficult to classify, especially with respect to the categories of well-differentiated neuroendocrine carcinomas (atypical carcinoids) and largecell neuroendocrine carcinomas. Some have advocated a grading system of 1, 2, and 3 for low-grade, intermediategrade, and high-grade neuroendocrine neoplasms, respectively. Others, such as Travis, favor the classification of typical carcinoid, atypical carcinoid, large-cell neuroendocrine carcinoma, and small-cell lung cancer, even though confusion exists in diagnosing atypical carcinoids, large-cell neuroendocrine carcinomas, and even small-cell carcinomas. Clinicians and pathologists should recognize there are neoplasms that show squamous and glandular differentiation composed of relatively small cells that can cause confusion
189 with neuroendocrine neoplasms, usually small-cell lung cancer. Basaloid carcinomas can frequently be misinterpreted as a neuroendocrine carcinoma. Finally, nonneuroendocrine neoplasms, specifically adenocarcinomas, squamous cell carcinomas, and large-cell undifferentiated carcinomas may express neuroendocrine markers by immunohistochemistry. The effect, if any, the morphologic and immunohistochemical features have on treatment of some neuroendocrine lung neoplasms has yet to be completely determined.
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