SDC1 and plasma cell myeloma: Based on the experiments of transplantation of bone marrow (BM) samples from MM patients into immunodeficient mice, so-called myeloma stem cells have been inferred to be present in CD19−/CD38++/CD138+ or CD138− plasma cell populations1,2; however, the results may indicate the presence of plasma cell populations with cell proliferation ability rather than the cellular origin of myeloma cells.