Human SET was originally identified as part of the SET-CAN fusion gene produced by a somatic translocation event in a patient with acute undifferentiated leukemia. In developing kidney, SET is highly expressed in the zone of nephron morphogenesis. SET has been shown to be a potent and specific inhibitor of protein phosphatase 2A, a family of major serine/threonine phosphatases involved in regulating cell proliferation and differentiation. SET is also involved in the regulation of renal cell proliferation and tumorigenesis. SET mRNA expression is markedly reduced in cells rendered quiescent by serum starvation, contact inhibition, or differentiation. SET protein expression is also much greater in developing rat and human kidney than in fully differentiated, mature kidney. High levels of SET mRNA and SET protein expression arefound in Wilms' tumor, but not in renal cell carcinoma, adult polycystic kidney disease or in transitional cell carcinoma.