Plasma Cell Neoplasm Mimicking Metastatic Bone Disease in a Breast Cancer Survivor: A Case Report Highlighting the Role of Serum Protein Electrophoresis.

Breast cancer, a prevalent solid tumor, is the most common cancer among women worldwide. Hematological malignancies, such as acute myeloid leukemia, myelodysplastic syndrome, and acute lymphoblastic leukemia, are more frequent in breast cancer survivors, while plasma cell neoplasms are less common. We report the case of a 44-year-old woman with breast cancer who underwent neoadjuvant chemotherapy and surgery, presenting one year later with bone lesions and anemia. Initially suspected to be metastatic bone disease, the findings of elevated serum total protein and globulins prompted serum protein electrophoresis, which revealed a distinct M band in the gamma region, suggesting a plasma cell neoplasm. Further evaluation confirmed this diagnosis, and treatment was initiated. This case underscores the importance of considering elevated total protein, globulins, and an altered albumin-to-globulin ratio as primary bone marrow disorders, such as plasma cell neoplasms, in breast cancer patients with bone lesions.