Beyond the Bone Marrow: Extramedullary Multiple Myeloma Mimicking Soft Tissue Tumors – A Case Series

Background: Extramedullary multiple myeloma (EMM) is an uncommon manifestation of multiple myeloma, characterized by the proliferation of malignant plasma cells outside the bone marrow. It occurs in approximately 7%–18% of patients and may involve soft tissues. Extramedullary lesions can mimic primary or metastatic soft tissue neoplasms, creating a diagnostic challenge. Case Series: We present a case series of patients with secondary extramedullary multiple myeloma presenting as unusual soft tissue masses. The lesions occurred at atypical sites and clinically and radiologically simulated other soft tissue tumors. Histopathological examination, supported by appropriate immunohistochemical evaluation, was essential for establishing the diagnosis of extramedullary plasma cell neoplasm. Conclusion: Extramedullary multiple myeloma should be considered in the differential diagnosis of an unexplained soft tissue mass. Recognition of its unusual presentations and appropriate use of histopathology and immunohistochemistry are crucial for accurate diagnosis. Early identification of extramedullary disease is clinically important because of its association with aggressive disease behavior and adverse prognosis.

Keywords: Extramedullary multiple myeloma; plasma cell neoplasm; extramedullary disease; soft tissue tumor; immunohistochemistry.