OPB-31121 inhibits the phosphorylation of STAT3 and STAT5 without upstream kinase inhibition and has beneficial effects in various types of hematopoietic malignancies, such as multiple myeloma; Burkitt lymphoma; and leukemia harboring BCR-ABL, FLT3/ITD, and JAK2 V61F oncokinases with their oncogenicities dependent on STAT3/5 [72]. Here, STAT3 is linked to plasma cell myeloma.