Track

Case Reports

Abstract

Primary cutaneous rhabdomyosarcoma (PCRMS) is exceedingly rare and includes various subtypes based on clinicopathological and genetic features (embryonal, alveolar, spindle cell/sclerosing, epithelioid, & pleomorphic). PCRMS has a bimodal age distribution with male predominance. Here, we present two pleomorphic PCRMS and discuss the differential diagnosis for this uncommon entity.

Dermatopathology archives were searched for PCRMS, resulting in the identification of two cases. Case 1 involved an 85-year-old male with a left index finger. Skin biopsy showed dermal spindle-shaped and pleomorphic cells, along with scattered rhabdomyoblasts (large rhabdoid cells with eccentric nuclei and abundant eosinophilic cytoplasm). Immunohistochemistry showed diffuse desmin expression, with focal MyoD1 and myogenin, whereas multiple melanocytic and keratinocytic markers were negative. Case 2 was from an 86-year-old male with a chest wall mass. Histological examination demonstrated a dermal and subcutaneous tumor composed of epithelioid and pleomorphic cells, mixed with rhabdomyoblasts. Tumor cells stained positive for desmin, myogenin, and MyoD1, but were negative for S100, SOX10, Melan-A, HMB45, BRAF, pankeratin, and ERG. 

Both cases of PCRMS presented in elderly males on sun-exposed sites exhibited pleomorphic morphology. The differential diagnosis of pleomorphic PCRMS includes dedifferentiated melanoma with rhabdomyoblastic differentiation, pleomorphic leiomyosarcoma, and undifferentiated pleomorphic sarcoma. Recognizing rhabdomyoblasts in a cutaneous pleomorphic tumor with desmin, MyoD1, and myogenin expression, and the absence of melanocytic differentiation by immunohistochemical and molecular studies, is essential for accurate diagnosis of PCRMS.