Primary cutaneous epithelioid rhabdomyosarcoma: a rare, recently described entity with review of the literature.

We report a case of a primary cutaneous epithelioid rhabdomyosarcoma that presented as a single raised pink-purple lesion (3.3 × 2.2 cm) on the left base of neck in a 75-year-old man. Histopathologic examination revealed an exophytic, nodular tumor within the dermis and superficial subcutis with overlying ulceration. The tumor exhibited sheet-like growth, infiltration of adjacent structures, and was composed of uniform epithelioid cells with abundant eosinophilic cytoplasm and eccentrically placed vesicular nuclei with irregular nuclear contours and prominent central nucleoli. Numerous mitotic figures were present [28/10 high power fields (HPF)] but only mild cytologic pleomorphism was identified. By immunohistochemistry, tumor cells were diffusely and strongly positive for desmin and MYOD1. Focal positive staining for myogenin and cytokeratin CK903 was identified. Stains for Melan-A, S-100, SOX10, p63 and CK5/6 were negative. These histopathologic and immunophenotypic features support a diagnosis of epithelioid rhabdomyosarcoma. No evidence of a deep soft tissue primary lesion was identified. In summary, epithelioid rhabdomyosarcoma can present as a primary cutaneous lesion and dermatopathologists should be aware of this entity.