Primary Parosteal Osteosarcoma of the Bone With Rhabdomyosarcomatous Features: A Rare Bone Tumour With a Pathological Dilemma

Primary osteosarcoma of the bone with rhabdomyosarcomatous characteristics constitutes a remarkably uncommon and distinct clinicopathological entity. This tumour exhibits a dual histological pattern, incorporating conventional osteosarcomatous morphology alongside rhabdomyosarcomatous cells, making diagnosis and management particularly challenging. We present a case of a 45-year-old woman with a progressively increasing painful mass in the proximal part of the leg. Radiological and histopathological investigations confirmed proximal tibial parosteal osteosarcoma exhibiting rhabdomyosarcomatous differentiation. The patient was treated with a multimodality approach involving above-knee amputation surgery followed by adjuvant chemotherapy. This clinical scenario highlights the importance of recognizing uncommon histological variants of osteosarcoma, as well as the future needs of additional research to develop standardized treatment algorithms and reliable prognostic indicators for this rare tumour.