- Email: [email protected]
Test and teach Number One Hundred And Three: Part 2
Pathology (2000 ) 32, pp. 225– 226
TEST AND TEACH Number One Hundred and Three: Part 2 See page 200 for figures and case details
EXPLANATION AND DIAGNOSIS PLEXIFORM FIBROHISTIOCYTIC TUMOR Plexiform fibrohistiocytic tumor typically occurs in young children. The most common sites of occurrence are the upper and lower extremities and the lesion is located in the deep dermis and subcutis.1– 5 The majority of tumors measure 1–3 cm in size, although the largest measured 8 cm. Gross examination showed a 2.5 ´ 1.8-cm grey–yellow fibrous nodule with irregular borders, which infiltrated into the surrounding fat and abutted the resection margins in a few areas. There were no areas of necrosis or hemorrhage. The overlying skin was not involved by tumor and there was no ulceration. Low-power microscopic examination reveals the characteristic biphasic and plexiform pattern of discrete rounded cellular nodules and short thick fascicles of spindled fibroblastic cells separated by fibrofatty tissue. The nodules are composed of bland mononuclear histiocytoid cells with ovoid vesicular nuclei and ample eosinophilic cytoplasm. Occasional multinucleate osteoclast-like giant cells are also interspersed within the nodules. The spindled cells within the fascicles show bland plump ovoid to elongated nuclei and eosinophilic cytoplasm. There is no mitotic activity, cytological atypia or necrosis. No vascular tumor emboli or perineural invasion are present. In some areas, the spindled and nodular areas appear to blend together. This intimate relationship between the two areas create the typical plexiform pattern of growth. A storiform pattern is not identified. Immunohistochemically, the cells of both tumor components show positive staining for the panhistiocytic marker CD68 and smooth muscle actin5– 7 . CD34 stains a few fibroblastic cells within the fascicles.10 There is no staining for S-100, desmin or keratins. Clinically, plexiform fibrohistiocytic tumors have been considered to have a low-grade malignant potential. The local recurrence rate varies from 35 to 40%. This is due to the fact that these tumors have infiltrative margins and excision may not be complete. There have been rare case reports of these tumors metastasising to regional lymph nodes and to the lung.8 Unfortunately, clinical aggressiveness cannot be correlated with histological features, such as the presence of vascular tumor emboli, mitotic activity or the predominance of any one tumor component. Flow cytometric studies5 on nine tumors showed all to be diploid. An interesting feature noted in this case is the presence of occasional CD34-positive fibroblastic cells within the
tumor fascicles. CD34 is known to mark “dendritic interstitial cells”9 within the dermis. Others have suggested that they represent tissue-specific differentiation forms of endothelial cells.10 In practice, CD34 also stains some myofibroblastic cells and cells of unusual tumors such as epithelioid sarcoma. In a study of 22 cases, Remstein et al. 5 have also found focal CD34 staining restricted to the fibroblastic tumor cells. The presence of CD34 staining, and indeed the general immunohistochemical features of plexiform fibrohistiocytic tumors, can be explained by noting that the histogenesis of these tumors is currently unsettled and is thought to involve a mixed proliferation of myofibroblasts, fibroblasts and macrophages. In its classical form, plexiform fibrohistiocytic tumor has few differential diagnoses. Plexiform neurofibromas and plexiform schwannomas lack the concomitant fascicular proliferation of cells and both stain positively for S100. A cutaneous myofibroma shows the typical zoning pattern with peripheral fascicular bundles and central round cell proliferation with a hemangiopericytic vascular pattern. Pilar leiomyomas and fibromatosis do not show the characteristic rounded nodules composed of histiocytoid cells and multinucleate giant cells. There is no staining for CD68. A cellular neurothelioma presenting with a nodular pattern can be excluded by the absence of giant cells and positive staining for NK1C3. Dermatofibromas usually occur in adults and show a solid growth pattern, lacking the characteristic plexiform growth. Many show a conspicuous storiform arrangement of spindle cells with scattered aggregates of xanthoma cells and siderophages. A giant cell malignant fibrous histiocytoma is often a much larger tumor and occurs in adults. There is diffuse nuclear pleomorphism, high mitotic activity, atypical mitotic figures, vascular tumor emboli and areas of tumor necrosis. While features such as high mitotic activity, rare atypical mitotic figures, moderate cellular atypia and intravascular growth have been identified in plexiform fibrohistiocytic tumors,5 they are very uncommon and are seen in a background of the more characteristic plexiform and biphasic growth pattern. Necrosis is not a feature of plexiform fibrohistiocytic tumors. References 1. Enzinger FM, Weiss SW. Soft Tissue Tumors, 3rd edn. St. Louis: Mosby, 1995: 343–6. 2. Enzinger FM, Zhang RY. Plexiform fibrohistiocytic tumor occurring in children and young adults: an analysis of 65 cases. Am J Surg Pathol 1988; 12: 81– 6.
ISSN 0031–3025 printed/ISSN 1465– 3931 online/00/030225 – 02 © 2000 Royal College of Pathologists of Australasia
226
TEST AND TEACH
3. Joseph AK, Tschen JA, Dickson JE. Long-standing subcutaneou s nodule in a young woman: plexiform fibrohistiocytic tumor. Arch Dermatol 1995; 131: 212–3, 215–6. 4. Zelger B, Weinlich G, Steiner H, et al. Dermal and subcutaneous variants of plexiform fibrohistiocytic tumor. Am J Surg Pathol 1997; 21: 235– 41. 5. Remstein ED, Arndt CAS, Nascimento AG. Plexiform fibrohistiocytic tumor: clinicopathologic analysis of 22 cases. Am J Surg Pathol 1999; 23: 662–70. 6. Holloway K, Holley MP, Fletcher CD. Plexiform fibrohistiocytic tumor: clinicopathological, immunohistochemical and ultrastructural analysis in favour of a myofibroblastic lesion. Histopathology 1991; 19: 503–13.
Pathology ( 2000 ), 32, August 7. Thomazy V, Nagy A, Gal I, Nemes Z. Plexiform fibrohistiocytic tumor with novel phenotypic features. Histopathology 1994; 25: 165–9. 8. Salomao DR, Nascimento AG. Plexiform fibrohistiocytic tumor with systemic metastases: a case report. Am J Surg Pathol 1997; 21: 469–76. 9. Suster S, Fisher C. Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors. Am J Surg Pathol 1997; 21: 195– 200. 10. Rudolph P, Schubert B, Wacker HH, et al. Immunophenotyping of dermal spindle cell tumors: diagnostic value of monocyte marker KiM1p and histogenic considerations. Am J Surg Pathol 1997; 21: 791– 800.
TEST AND TEACH Number One Hundred and Three: Part 2 See page 200 for figures and case details
EXPLANATION AND DIAGNOSIS PLEXIFORM FIBROHISTIOCYTIC TUMOR Plexiform fibrohistiocytic tumor typically occurs in young children. The most common sites of occurrence are the upper and lower extremities and the lesion is located in the deep dermis and subcutis.1– 5 The majority of tumors measure 1–3 cm in size, although the largest measured 8 cm. Gross examination showed a 2.5 ´ 1.8-cm grey–yellow fibrous nodule with irregular borders, which infiltrated into the surrounding fat and abutted the resection margins in a few areas. There were no areas of necrosis or hemorrhage. The overlying skin was not involved by tumor and there was no ulceration. Low-power microscopic examination reveals the characteristic biphasic and plexiform pattern of discrete rounded cellular nodules and short thick fascicles of spindled fibroblastic cells separated by fibrofatty tissue. The nodules are composed of bland mononuclear histiocytoid cells with ovoid vesicular nuclei and ample eosinophilic cytoplasm. Occasional multinucleate osteoclast-like giant cells are also interspersed within the nodules. The spindled cells within the fascicles show bland plump ovoid to elongated nuclei and eosinophilic cytoplasm. There is no mitotic activity, cytological atypia or necrosis. No vascular tumor emboli or perineural invasion are present. In some areas, the spindled and nodular areas appear to blend together. This intimate relationship between the two areas create the typical plexiform pattern of growth. A storiform pattern is not identified. Immunohistochemically, the cells of both tumor components show positive staining for the panhistiocytic marker CD68 and smooth muscle actin5– 7 . CD34 stains a few fibroblastic cells within the fascicles.10 There is no staining for S-100, desmin or keratins. Clinically, plexiform fibrohistiocytic tumors have been considered to have a low-grade malignant potential. The local recurrence rate varies from 35 to 40%. This is due to the fact that these tumors have infiltrative margins and excision may not be complete. There have been rare case reports of these tumors metastasising to regional lymph nodes and to the lung.8 Unfortunately, clinical aggressiveness cannot be correlated with histological features, such as the presence of vascular tumor emboli, mitotic activity or the predominance of any one tumor component. Flow cytometric studies5 on nine tumors showed all to be diploid. An interesting feature noted in this case is the presence of occasional CD34-positive fibroblastic cells within the
tumor fascicles. CD34 is known to mark “dendritic interstitial cells”9 within the dermis. Others have suggested that they represent tissue-specific differentiation forms of endothelial cells.10 In practice, CD34 also stains some myofibroblastic cells and cells of unusual tumors such as epithelioid sarcoma. In a study of 22 cases, Remstein et al. 5 have also found focal CD34 staining restricted to the fibroblastic tumor cells. The presence of CD34 staining, and indeed the general immunohistochemical features of plexiform fibrohistiocytic tumors, can be explained by noting that the histogenesis of these tumors is currently unsettled and is thought to involve a mixed proliferation of myofibroblasts, fibroblasts and macrophages. In its classical form, plexiform fibrohistiocytic tumor has few differential diagnoses. Plexiform neurofibromas and plexiform schwannomas lack the concomitant fascicular proliferation of cells and both stain positively for S100. A cutaneous myofibroma shows the typical zoning pattern with peripheral fascicular bundles and central round cell proliferation with a hemangiopericytic vascular pattern. Pilar leiomyomas and fibromatosis do not show the characteristic rounded nodules composed of histiocytoid cells and multinucleate giant cells. There is no staining for CD68. A cellular neurothelioma presenting with a nodular pattern can be excluded by the absence of giant cells and positive staining for NK1C3. Dermatofibromas usually occur in adults and show a solid growth pattern, lacking the characteristic plexiform growth. Many show a conspicuous storiform arrangement of spindle cells with scattered aggregates of xanthoma cells and siderophages. A giant cell malignant fibrous histiocytoma is often a much larger tumor and occurs in adults. There is diffuse nuclear pleomorphism, high mitotic activity, atypical mitotic figures, vascular tumor emboli and areas of tumor necrosis. While features such as high mitotic activity, rare atypical mitotic figures, moderate cellular atypia and intravascular growth have been identified in plexiform fibrohistiocytic tumors,5 they are very uncommon and are seen in a background of the more characteristic plexiform and biphasic growth pattern. Necrosis is not a feature of plexiform fibrohistiocytic tumors. References 1. Enzinger FM, Weiss SW. Soft Tissue Tumors, 3rd edn. St. Louis: Mosby, 1995: 343–6. 2. Enzinger FM, Zhang RY. Plexiform fibrohistiocytic tumor occurring in children and young adults: an analysis of 65 cases. Am J Surg Pathol 1988; 12: 81– 6.
ISSN 0031–3025 printed/ISSN 1465– 3931 online/00/030225 – 02 © 2000 Royal College of Pathologists of Australasia
226
TEST AND TEACH
3. Joseph AK, Tschen JA, Dickson JE. Long-standing subcutaneou s nodule in a young woman: plexiform fibrohistiocytic tumor. Arch Dermatol 1995; 131: 212–3, 215–6. 4. Zelger B, Weinlich G, Steiner H, et al. Dermal and subcutaneous variants of plexiform fibrohistiocytic tumor. Am J Surg Pathol 1997; 21: 235– 41. 5. Remstein ED, Arndt CAS, Nascimento AG. Plexiform fibrohistiocytic tumor: clinicopathologic analysis of 22 cases. Am J Surg Pathol 1999; 23: 662–70. 6. Holloway K, Holley MP, Fletcher CD. Plexiform fibrohistiocytic tumor: clinicopathological, immunohistochemical and ultrastructural analysis in favour of a myofibroblastic lesion. Histopathology 1991; 19: 503–13.
Pathology ( 2000 ), 32, August 7. Thomazy V, Nagy A, Gal I, Nemes Z. Plexiform fibrohistiocytic tumor with novel phenotypic features. Histopathology 1994; 25: 165–9. 8. Salomao DR, Nascimento AG. Plexiform fibrohistiocytic tumor with systemic metastases: a case report. Am J Surg Pathol 1997; 21: 469–76. 9. Suster S, Fisher C. Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors. Am J Surg Pathol 1997; 21: 195– 200. 10. Rudolph P, Schubert B, Wacker HH, et al. Immunophenotyping of dermal spindle cell tumors: diagnostic value of monocyte marker KiM1p and histogenic considerations. Am J Surg Pathol 1997; 21: 791– 800.