A case report of secondary synchronous diagnosis of multiple myeloma and systemic lupus erythematosus after breast cancer treatment: A CARE-compliant article.

Introduction: Breast cancer (BC) is the most diagnosed cancer worldwide. Multiple myeloma (MM) is a hematologic malignancy characterized by the overproduction of monoclonal antibodies in the bone marrow. Systemic lupus erythematosus (SLE) is distinguished by the aberrant activity of the immune system with heterogeneous clinical manifestations.