Concurrent Multiple Myeloma and Osteosarcoma of the Mandible – An Extremely Rare Case Report

Coexistence of multiple myeloma (MM) and osteosarcoma (OS) in the mandible represents an extremely uncommon dual malignancy, with only three cases reported worldwide. This report describes a 30-year-old female presenting with concurrent MM and OS involving the left mandible a challenging diagnostic overlap between a hematologic and an osteogenic neoplasm. The patient exhibited progressive facial swelling and tooth mobility. Radiographic and computed-tomographic (CT) findings revealed extensive osteolytic destruction with cortical perforation. Laboratory investigations confirmed monoclonal gammopathy and Bence-Jones proteinuria, while histopathology demonstrated sheets of plasma cells admixed with malignant osteoid-forming cells. Integration of radiological, hematological, and microscopic features established the diagnosis of concurrent MM and OS. This case highlights the critical importance of a multidisciplinary diagnostic approach in evaluating atypical jaw lesions.