MELK and plasma cell myeloma: It was demonstrated over 25 years ago that malignant MM precursor cells exist in the peripheral blood and can be induced to proliferate and differentiate into clonal MM PC with interleukin-3 (IL-3) and IL-6 treatment.15 Given the increasing evidence suggesting a role for MELK in cancer stem cells,3 we sought to determine the effects of OTS167 on the outgrowth and differentiation of presumptive myeloma stem cells into MM PC.