Alveolar rhabdomyosarcoma with pre-therapy maturation

Abstract

Abstract Introduction/Objective Alveolar rhabdomyosarcoma (ARMS) is the second most common type of rhabdomyosarcoma in children and adolescents. Common locations include the head and neck, trunk, extremities, and pelvic area. They are a prototypical round cell sarcoma and are treated with multimodality therapy. The purpose of this report is to describe a case of this tumor showing unusual rhabdomyoblastic differentiation which is most commonly seen in post- therapy setting but is almost unheard of pre-therapy. Methods/Case Report A three-year-old male presented with painless, right lower extremity mass. It was noticed two months prior and had been rapidly growing since then. Incisional biopsy was performed. Histologic sections showed a round cell sarcoma with an alveolar growth pattern. Variably mature single- and multinucleated rhabdomyoblasts with ample eosinophilic cytoplasm were present throughout the biopsy specimen. On immunostains, the tumor cells were positive for desmin, MyoD1, as well as myogenin (minor subset) and negative for pancytokeratin, CD45 and WT-1, strongly supporting the diagnosis of ARMS. FISH studies showed the presence of FOXO1 (FKHR) rearrangement, further confirming diagnosis.The patient received chemotherapy, radiotherapy, and surgery. On follow-up after six months, the patient was well with no significant complications. Results (if a Case Study enter NA) N/A Conclusion Post-chemotherapy rhabdomyoblast differentiation is commonly seen and documented in literature, potentially signifying increased response of tumor cells to therapy. Our case highlights that such changes can also be seen pre-treatment and must not sway the pathologist from diagnosis of ARMS.