Case Reports

Epithelioid Sarcoma Resembling Benign Fibrous Histiocytoma

Cutis. 2015 February;95(2):83-86

References

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Epithelioid sarcoma is a mesenchymal tumor that can display multidirectional differentiation that is primarily epithelial.¹⁶ The precise histogenesis of ES remains unclear, but studies have demonstrated a spectrum of differentiation that ranges from primitive myofibroblast or fibrohistiocytelike cells to those with well-developed epithelial properties.^16,17 Epithelioid sarcoma characteristically coexpresses vimentin and low-molecular-weight CKs such as cell adhesion molecule 5.2. The tumor cells often are immunoreactive for epithelial membrane antigen and more than 50% of cases exhibit remarkable CD34 positivity.¹⁶ More recent studies have further refined the immunophenotype, demonstrating frequent expression of CK8 and CK19 but less commonly CK7, CK20, CK34bE12, and CK5/6.^18-20 Additional studies reported that in 10 of 11 cases, ES was positive for CA 125 on immunohistochemical staining, and 3 of 5 patients also had elevated serum CA 125 levels.^21,22 More recently, Hoshino et al²³ showed elevated serum CA 125 levels in 5 of 7 patients with ES. Cancer antigen 125 is a high-molecular-weight glycoprotein commonly used in the identification of epithelial ovarian carcinomas; however, it also has been described in a number of other neoplasms including carcinomas of the breast, lungs, and colon and lymphoma.^24-27 Although it appears that the addition of CA 125 to a panel of other immunohistochemical stains may be helpful in differentiating ES from other soft tissue sarcomas and serum CA 125 levels may help determine tumor burden, currently the number of cases studied is too small to definitively make that conclusion.^21,23 In our case, the tumor cells were strongly and diffusely positive for CA 125. Serum CA 125 levels were not available.

^{Figure 3. Tumor cells focally showed strong membranous staining for cytokeratin AE1/AE3 (original magnification ×400).}

^{Figure 4. High-power view of the tumor from the amputation specimen showed sheets of epithelioid and polygonal cells displaying marked nuclear pleomorphism and scattered mitoses (H&E, original magnification ×400).}

Cytogenetic studies have failed to identify a consistent chromosomal abnormality in ES.⁵ Some analyses performed by comparative genomic hybridization on isolated cases and small case series indicate that the most frequent alterations involve 8q, 18q11, and 22q11.^13,28,29 The tumor suppressor gene SMARCB1/INI1 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily B, member 1/integrase interactor 1) has been mapped to 22q11, and ES commonly shows absence of nuclear staining for this protein, indicating inactivation.^13-15

Conclusion

Benign fibrohistiocytic proliferations should be included in the differential of histological mimickers of ES. Deep biopsies are essential to differentiate these benign tumors from fibrous histiocytomalike or fibromalike lesions of ES because superficial portions of ES may be well differentiated.