Bilateral Breast Involvement in Multiple Myeloma: A Report of a Rare Case.

Breast plasmacytoma is an uncommon extramedullary manifestation of multiple myeloma (MM). This case presents a primary extramedullary plasmacytoma and progression to MM with breast involvement after 12 years of discovering the disease. The patient is a 54-year-old woman who initially presented with a right humerus pathological fracture that turned out to be a primary extramedullary plasmacytoma. She received chemotherapy and achieved remission. Six years later, the disease recurred as a mass in the sternum, which was treated with radiation and chemotherapy but without improvement. The disease then progressed to MM with lesions in various bones. Following the first radiation treatment, the patient developed a new-onset cough, leading to a high-resolution CT, which incidentally revealed multiple bilateral breast lesions suggestive of malignancy. Mammography and sonography indicated multiple nodular densities warranting biopsy. Tru-cut biopsy confirmed plasmacytic neoplasm consistent with MM. Subsequent imaging showed the progression of breast lesions with increasingly aggressive features. Biopsies consistently indicated refractory progressive MM. This case highlights the aggressive, multisystemic nature of MM and the challenge of managing refractory disease with extensive systemic involvement, including rare bilateral breast lesions.