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...