Proximal-type epithelioid sarcoma: report of two cases in the perineum: differential diagnosis and review of soft tissue tumors with epithelioid and/or rhabdoid features.

The authors report two cases of perineal proximal-type epithelioid sarcoma in middle-aged men, age 51 and 43 years old. Both tumors were located in the right side. In the first patient a 7.5-cm, well-encapsulated tumor was completely excised. The second patient was a referral case with incomplete excision, but the computed tomography scan and magnetic resonance imaging showed a 14-cm nonencapsulated tumor involving the soft tissues of the inner thigh and perineum, as well as metastasis in right inguinal and retroperitoneal lymph nodes. Both neoplasms had a predominant solid pattern alternating with occasional discohesive areas. Both were composed of large oval to polygonal cells with vesicular nuclei, conspicuous nucleoli, and amphophilic to eosinophilic cytoplasm. Rhabdoid phenotype was identified in the second case only. The first neoplasm displayed 15% necrosis, 7 mitoses per 10 high-power field, focal vascular invasion, and no extracapsular invasion. The other exhibited 60% necrosis, 12 mitoses per 10 high-power fields, extensive vascular invasion, no distinct capsule, and invasion of the surrounding fatty tissue. Both were positive for vimentin, cytokeratin, epithelial membrane antigen, and CD34. Muscle-specific actin was negative in the first case and focally positive in the second. CD56 was positive in the second case and negative in the first case. Desmin, CD45, CD30, factor VIII, CD31, S100, HMB45, calretinin, and synaptophysin were negative in both. Since proximal-type epithelioid sarcoma can be confused with a number of other soft tissue tumors with epithelioid and/or rhabdoid features, the authors emphasize the immunohistochemical differential diagnosis.