PTPA and breast cancer: In CML, PP2A is inhibited by SET4 and cancerous inhibitor of PP2A (CIP2A).5 CIP2A inhibits PP2A activity and functions by preventing PP2A-driven dephosphorylation and stabilization of c-Myc.6, 7, 8 CIP2A is a strong prospective predictor of subsequent development of BC in imatinib-treated CML patients,5 although the underlying mechanisms remain unclear.