Refractory multiple myeloma with extramedullary plasmacytoma of the spleen and suspicious teratoma: a rare case report and literature review.

Multiple myeloma (MM) is a type of malignant disease that is characterized by a clonal proliferation of plasma cells within the bone marrow. Relapsed and refractory multiple myeloma (RRMM) is a subtype of MM that is unreactive to salvage therapy and progresses during treatment or within 60 days of the last therapy in patients who achieved a minimal response before progression of disease. This usually results in a poor prognosis. Extramedullary plasmacytoma (EMP) occurs when MM occasionally develops in tissues other than bones marrow. To the best of our knowledge, case studies of the presence of EMPs in the spleen have rarely been reported. Teratoma is a type of congenital tumor that consists of tissue that arises from pluripotent embryonic cells. Here we report a case of refractory immunoglobulin G (IgG) MM with both splenic plasmacytomas and a suspicious teratoma. To investigate the clinical and treatment features of patients under similar conditions, we also reviewed the available literature supporting the useful information in the pathogenesis, diagnosis and treatment of RRMM with EMP.