Spatially fractionated (GRID) radiotherapy in a patient with metastatic pleomorphic rhabdomyosarcoma: a case report

Adult pleomorphic rhabdomyosarcoma is an exceedingly rare, aggressive, high-grade soft tissue sarcoma with a poor prognosis. Treatment for metastatic pleomorphic rhabdomyosarcoma typically involves a combination of chemotherapy, radiation, and surgical resection, though optimal treatment strategies remain undefined. We present here a case of a 52-year-old otherwise healthy male who was diagnosed with metastatic pleomorphic rhabdomyosarcoma with a rapidly progressive, bulky, and symptomatic left upper back tumor. He was treated with multi-line systemic chemotherapy, spatially fractionated (GRID) radiotherapy to his primary back tumor, stereotactic body radiotherapy (SBRT) to his metastatic lung nodule, and long-term maintenance pazopanib, achieving a durable partial response followed by sustained disease control exceeding four years. Adult pleomorphic rhabdomyosarcoma remains a difficult cancer to treat, and more research is needed to better understand its disease course and optimal treatment regimens. This case highlights the potential role of GRID radiotherapy as a component of treatment for bulky, unresectable tumors and underscores the need for further investigation of this modality in aggressive soft tissue sarcomas.