CD-34 and keratin expression distinguishes solitary fibrous tumor (Fibrous mesothelioma) of pleura from desmoplastic mesothelioma

CD-34 and Keratin Expression Distinguishes Solitary Fibrous Tumor (Fibrous Mesothelioma) of Pleura From Desmoplastic Mesothelioma ANDREW FLINT, MD AND SHARON W. WEISS, MD Solitary fibrous tumors (sFrs) often involve the pleura and also may encompass the peritoneum and nonserosal sites. On occasion SFTs mimics other neoplasms, including desmoplastic mesothelioma. CD-34, initially characterized as a hematopoietic progenitor cell antigen, recently has been identified in a small number of SFFs. Based on this observation, we compared the keratin, vimenfin, and CD-34 expression of 19 SFFs and eight desmoplastic mesotheliomas. Fifteen of 19 SFTs (78.9%) expressed CD-34, whereas keratin expression was absent in all s g r s . In contrast, none of the desmoplastic mesotheliomas expressed CD-34 and keratin expression was found in seven of

eight (87.5%). Vhnentin expression was noted in 18 of 19 SFFs and in seven of eight desmoplastic mesotheliomas. We conclude that CD34 expression distinguishes SFF from desmoplastic mesothelioma. Additionally, the results of our study support the idea that s F r is not derived from or related to conventional mesothelinm. HUM PATHOL 26:428--431. Copyright © 1995 by W.B. Saunders Company Key words: pleura, fibrous tumors, CD-34. Abbreviations: SFF, solitary fibrous tumor; HE, hematoxylin-eosin; HPFs, high power fields.

Solitary fibrous t u m o r s (SFTs) m o s t often involve the pleura, a l t h o u g h the p e r i t o n e u m as well as n o n s e r o sal sites are infrequently e n c o m p a s s e d . 14 W h e n involving the pleura, SFT is usually a well circumscribed, fibrous mass o f variable cellularity. T h e pleural SFT also has b e e n t e r m e d fibrous m e s o t h e l i o m a , b e n i g n mesothelioma, localized m e s o t h e l i o m a , subpleural fibroma, a n d localized fibrous t u m o r o f the pleura. 5 T h e line o f differentiation o f SFT is u n k n o w n a n d b o t h mesothelial a n d m e s e n c h y m a l differentiation have b e e n postulated. ~]2 Most i m m u n o h i s t o c h e m i c a l studies o f SFT have evaluated either keratin or vimentin expression. 1~15 CD-34, initially characterized as a h e m a t o p o i e t i c prog e n i t o r cell antigen, l~as recently has b e e n d e t e c t e d in endothelial cells a n d vascular n e o p l a s m s as well as in certain connective tissue cells f o u n d in the skin. 19zl T h e r e c e n t study by Weiss a n d Nickoloffzl identifying this antigen in a limited n u m b e r o f SFTs p r o m p t e d us to study the expression o f CD-34 in a larger n u m b e r o f SFTs a n d to evaluate the utility o f CD-34 expression in differentiating SFT f r o m desmoplastic m e s o t h e l i o m a , a histologically similar neoplasm.

fixed, paraffin-embedded samples. The HE-stained sections were examined and the following features evaluated: degree of cellularity (1 to 4+); number of mitotic figures (mitotic figures per 10 high power fields [HPFs; 10X ocular, 40X objective]); presence of fibrosis, calcification, or adjacent mesothelial surface; and nuclear pleomorphism (1 to 3+). Criteria of malignancy were similar to those of England et al ~5and include marked cellularity with crowding and overlapping of nuclei, increased mitotic activity (>4 mitotic figures/ 10 HPFs), and nuclear pleomorphism. Each unstained section was dehydrated in xylene and rehydrated before being stained with immunoperoxidase. For CD-34 staining a 1:10 dilution of the primary antibody (antiHPCA-1 [clone My 10], Becton Dickinson, San Jose, CA) was employed. An avidin-biotin peroxidase technique (Vectastain Kit, Vector Laboratories, Burlingame, CA) was used; 3,3-diaminobenzidine was used to produce a brown reaction product. A 1% hematoxylin counterstain was used in all samples. Positive and negative controls were included for staining. Vimentin (Dako, Carpinteria, CA) and keratin (K576, Dako; AEI/AE3, Boehringer Mannheim, Indianapolis, IN) staining was carried out in similar fashion. Microwave/citrate buffer antigen retrieval was not used. The percentage of positively stained cells was recorded for each antigen.

MATERIALS AND METHODS

RESULTS

Nineteen cases of SFT were culled from our consultation files. For comparison purposes eight cases of desmoplastic mesothelioma were selected. The site of each tumor was recorded from the consultation correspondence; however, tumor size was mentioned in only two instances. For each case four-micra-thick, hematoxylin and eosin (HE)-stained and unstained histological sections were prepared from formalin-

O f the 19 SFTs, 11 arose f r o m pleural surfaces, three f r o m the m e d i a s t i n u m , two f r o m the inguinal region, a n d o n e each f r o m the p e r i t o n e u m , paraspinal area, a n d pyriform sinus. Regardless o f site, the SFTs manifested similar histological features. T h e n e o p l a s m s were c o m p o s e d o f spindle cells usually a r r a n g e d in short, irregular fascicles often situated a r o u n d ectatic vessels s o m e w h a t similar to a h e m a n g i o p e r i c y t o m a . Occasionally, however, the fascicles were long. Characteristically b e n i g n t u m o r s c o n t a i n e d p r o m i n e n t areas o f collagenization so that it was n o t u n c o m m o n to find dense mats o f collagen that crisscrossed o n e a n o t h e r in a basket weave fashion (Fig 1). T h e nuclei were fusiform a n d p l e o m o r p h i s m was n o t p r o m i n e n t in m o s t tumors. T h e cellularity varied f r o m t u m o r to t u m o r b u t usually was

From the Department of Pathology, The University of Michigan School of Medicine, Ann Arbor, MI. Accepted for publication August 2, 1994. Address correspondence to Andrew Flint, MD, Department of Pathology, University of Michigan Hospitals, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0054. Copyright © 1995 by W.B. Saunders Company 0046-8177/95/2604-001255.00/0

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SOLffARY FIBROUS TUMORS (Flint & Weiss)

FIGURE 1. (A) Solitary fibrous tumor of pleura. Neoplastic cells are scattered among bundles of collagen arranged in a basket w e a v e pattern. (HE stain; original magnification x165.) (B) Solitary fibrous tumor of pleura. Tumor nuclei manifest a variety of shapes, although the chromatin pattern is uniform. Nucleoli and mitotic figures are not evident in this view. (HE stain; original magnification x330.)

modest. Hypercellular areas alternated with paucicellular regions and myxoid regions also were encountered. With four exceptions, mitotic figures ranged from 0 to 2/10 HPFs. Areas of fibrosis or hyalinization were present in all tumors. Five neoplasms were j u d g e d malignant in view of d o c u m e n t e d liver metastases (one tumor) or extensive necrosis, large numbers of mitotic figures (i>4 mitotic figures/10 HPFs), and increased (4+) cellularity (four tumors). Size measurements were not available, save for two malignant SFTs ( > 9 cm). A mesothelial surface adjacent to neoplasm was not noted in any tumor. All eight samples of desmoplastic mesothelioma manifested cellular atypia (Fig 2) and often contained irregular foci of necrosis. 22 '23 Vimentin expression was n o t e d in 13 of the 14 benign SFTs (93%) and in all of the malignant SFTs. Keratin expression was absent in all SFTs. CD-34 expression was observed in all of the malignant SFTs and in 10 of 14 benign SFTs (77%) (Fig 3). In all but two tumors at least one third of the cells stained strongly for CD-34. O f the desmoplastic mesotheliomas, one did not express vimentin and a n o t h e r did not express keratin. All o t h e r tumors were positive for vimentin and keratin. CD-34 expression was not detected in any tumor. These reSults are summarized in Table 1.

Stout and Murray 6 as well as Sano et a125 postulated a mesothelial origin for the localized form. Although ultrastructural studies of SFT have described features of mesothelial differentiation, 5'8'12 other investigations have shown only primitive mesenchymal fibroblastic cells without evidence of mesothelial differentiat i o n . 13'14'26 Subsequently, SFT has been described in sites not usually associated with serosal surfaces, including the nasal cavity, paranasal sinuses, nasopharynx, liver, and epiglottis. ~4 The results of our study provide additional support for the idea that the SFF is not derived from or related to conventional mesothelium. Nearly 80% of SFTs strongly expressed CD-34, but n o n e expressed keratin.

DISCUSSION A variety of terms have been applied to the SFT, including localized fibrous mesothelioma, localized fibrous tumor of the pleura, and submesothelioma. 24 Since the early report by Klemperer and Rabin, 11 SFT has received the most attention as a pleural neoplasm. Klemperer and Rabin divided pleural neoplasms into diffuse and localized forms. They postulated that diffuse neoplasms arose from a multipotential mesothelial cell (a true " m e s o t h e l i o m a " ) and the localized form arose from subpleural mesenchymal cells. Somewhat later,

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FIGURE 2. Desmoplastic mesothelioma. Cells with enlarged hyperchromatic nuclei lie entrapped within a collagenous stroma. Note that other nuclei are less conspicuous and resemble those found in solitary fibrous tumor (Fig 1). (HE stain; original magnification x 165.)

HUMAN PATHOLOGY

Volume 26, No. 4 (April 1995)

These results are similar to those r e p o r t e d in abstract f o r m by Renshaw et al. 27 O t h e r investigators have consistently n o t e d the absence of keratin within these lesions. 2'13'14 In contrast, 90% of the mesotheliomas in o u r series expressed vimentin and keratin, but n o n e contained CD-34-positive cells. T h e absence of keratin expression in one of the mesotheliomas is u n e x p e c t e d because keratin immunoreactivity has b e e n r e p o r t e d in desmoplastic mesothelioma, z8 As with all of the other consultation cases, the details concerning the fixation of the tissue were not known. Antigen retrieval techniques were not employed for this case; had they been, such techniques may have revealed keratin expression. Expression of CD-34 by SFFs may not be d e p e n d e n t on the degree of differentiation because the antigen was easily detected within even the most malignant areas of these neoplasms. O u r study also endorses the current belief that SFT is not restricted to serosal surfaces but may be found in diverse locations. All SFTs in o u r study that arose in the mediastinum (three), inguinal region (two), and pyriform sinus (one) expressed CD-34 to the same degree as those tumors of the pleura. Until now, this hypothesis was s u p p o r t e d by the somewhat subjective observations that similar tumors in diverse sites shared a sufficient n u m b e r of histological similarities to consider them a c o m m o n entity. T h e expression of CD-34 now serves as an i n d e p e n d e n t means of confirming this idea. T h e r e seems to be an e m e r g i n g consensus that the SFT arises from a submesothelial cell 15'29'~° that has b e e n variously r e g a r d e d by Bolen et al as a primitive fibroblast or mesenchymal cell 3x'32 or by Craighead as a primitive multipotential cell. 33 O t h e r evidence that supports this postulate is the observation by Raftery that mesothelium may originate f r o m submesothelial connective tissue a f t e r injury. 34 Skin and Firminger 35 postulated that both surface mesothelial cells and submesothelial connective tissue cells may have a role in the histogenesis of mesothelioma.

FIGURE 3. Solitary fibrous tumor. Numerous spindle cells stain positively for CD-34, Endothelial cells also stain positively. (Immunoperoxidase stain; original magnification x165.)

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TABLE I .

Immunohistochemical Profile of SFT a n d Desmoplastic Mesothelioma

Diagnosis SFT (n = 19) Desmoplastic mesothelioma (n = 8)

Vimentin Positive

Keratin Positive

CD-34 Positive

18/19

0/19

15/19

7/8

7/8

0/8

T h e expression o f CD-34 does not provide information as to the exact line of differentiation for the SFT because it does not a p p e a r to be lineage specific. However, some investigators postulate that CD-34 may define populations of cells able to serve as precursors or progenitors i n d e p e n d e n t o f site or line of differentiation. 21 For example, CD-34 defines a resident population of CD-34-positive dendritic cells that surround the bulge portion of the hair shaft within normal skin. 2° Although originally described as a hematopoietic progenitor cell antigen, this t r a n s m e m b r a n e glycoprotein has b e e n localized to an increasing n u m b e r of different tissues, including endothelium, perifollicular cells of the hair shaft, dendritic dermal cells, and a subset of e n d o n e u r i a l cells. 19'2° A n u m b e r of mesenchymal tumors, including d e r m a t o f i b r o s a r c o m a and some benign nerve sheath tumors, also contain immunoreactive CD-34. 2] Regardless of these lingering questions concerning the lineage of SFT, CD-34 appears to be an empirically useful antigen to discriminate SFT f r o m desmoplasfic mesothelioma, two lesions that could cause diagnostic problems, especially in the context of limited biopsy material.

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