KIT and gastrointestinal stromal tumor: Protein kinases are the most prominent group of HSP90 clients and are recruited to the molecular chaperone by the kinase-specific cochaperone CDC37 (cell division cycle 37).34 Our previous studies have shown that CDC37 is a crucial HSP90 cofactor for KIT oncogenic expression in GIST.35 Opportunities for more selective HSP90 targeting might result from pharmacologic dysregulation of CDC37, in particular by modulation of CDC37 activation by phosphorylation at the Ser 13 residue.