Pleomorphic rhabdomyosarcoma: diagnostic considerations and case report

Pleomorphic rhabdomyosarcoma is a rare entity almost exclusively in older adults and portends aggressive disease with early metastasis. Pleomorphic rhabdomyosarcoma predominantly arises in the soft tissue of lower extremities and presents as a rapidly enlarging, deep soft tissue swelling. Although the aetiology is unknown, these sarcomas have complex karyotypes without a consistent molecular abnormality. Histologically, these tumours contain sheets of pleomorphic sheets of multinucleated polygonal, rhabdoid or spindled cells with an eosinophilic cytoplasm. Immunohistochemically these tumours are typically positive for desmin, myogenin, MYOD1 and are negative for melanocytic markers such as S100 and SOX10. We present a rare case of chest wall pleomorphic rhabdomyosarcoma in a 78-year-old male with a prior history of melanoma and discuss the key diagnostic considerations.