Multifocal Osteosarcoma: Multiple Primaries or Metastases? A Report of Rare Case and Review of Literature

INTRODUCTION: Multifocal osteosarcoma (MFOS) is characterized by multicentricity of osseous osteosarcomas, either synchronous or metachronous, without visceral involvement. They account for about 1.5% of all osteosarcomas. Most synchronous MFOS has one dominant lesion with one to four and very rarely five or more secondary lesions. The distal femur followed by the proximal tibia is the most common site of dominant lesions. Its prognosis remains extremely poor even with combined chemotherapy and surgery. CASE REPORT: We describe a rare case of MFOS in a 10-year-old boy who presented with a short history of severe aching pain in the right lower limb following a trivial fall. Initial workup and relevant investigations revealed a synchronous multicentric osteosarcoma with extensive involvement of appendicular and axial skeletal system. The dominant lesion was at the lower end of the right femur with multiple secondary lesions in the right tibia, left femur, bilateral humeri, pelvis, cervical and dorsolumbar spine, ribs, and sternum. The patient received one cycle of doxorubicin and cisplatin-based chemotherapy but unfortunately succumbed to progressive disease, a month after initiation of chemotherapy. CONCLUSION: MFOS is a very rare presentation of osseous osteosarcoma. The non-specific clinical manifestation, despite the presence of generalized skeletal involvement, presents a diagnostic difficulty for both the clinician and the radiologist. Only biopsy and histopathological examination can confirm the diagnosis of this highly malignant disease and help in proper management.