This study evaluates CLR 131 in patients with select B-cell malignancies (multiple myeloma( MM), indolent chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL), lymphoplasmacytic lymphoma (LPL), marginal zone lymphoma (MZL), mantle cell lymphoma (MCL), and diffuse large B-cell lymphoma (DLBCL) who have been previously treated with standard therapy for their underlying malignancy.