Multiple Myeloma Complicating Breast Cancer During Treatment: A Case Report

Research Background: Breast cancer is a malignant tumor that threatens women's health. Among breast cancer patients, about 4.2% to 17% may suffer from multiple primary malignant neoplasms. Cases of patients suffering from both breast cancer and multiple myeloma are relatively rare in clinical practice. This paper reports one case of a patient who developed multiple myeloma during the treatment of breast cancer. Clinical Data: The patient was a 56-year-old female, admitted to hospital due to "fever for 4 days, one year after the treatment of left breast cancer". The patient was diagnosed with left breast cancer (ypT1N1M0, HER2-overexpressing subtype) approximately one year prior to presentation. Following diagnosis, the patient was treated sequentially with TcbHP and THP chemotherapy regimens, and subsequently received local radiotherapy. The patient developed fever four days prior to admission. Further laboratory examinations revealed pancytopenia, positive IgA-λ-type monoclonal immunoglobulin by immunofixation electrophoresis, and myeloma cells accounting for 11% in bone marrow smears. Bone marrow immunophenotyping indicated abnormal plasma cells, and pathological results of bone marrow biopsy were consistent with multiple myeloma. The final diagnosis was breast cancer complicated with multiple myeloma. After confirmed diagnosis, the patient was transferred to another hospital for targeted treatment of multiple myeloma and has been receiving continuous treatment there up to the time of follow-up. Conclusions: For patients with breast cancer, if they develop bone pain, anemia, hypercalcemia or renal dysfunction that cannot be explained by tumor metastasis or conventional complications after surgery or during follow-up, clinicians should be alert to the possibility of second primary tumors.