CDK4 and neoplasm: At present, a number of Hsp90 molecular chaperones have been identified with possible implications on the proliferation and apoptosis of tumor cells, including Bcl-2, AKT/PKB, survivin, c-Raf, JNK, pp60 (v-src), Bcr-Abl, mutant p53, ErbB2 (Her-2), Flt3, HIF-1α, B-Raf and CDK4 (19,20).