CDK4 and endometrial cancer: However, there are clinical trials evaluating palbociclib, a CDK4/6 specific inhibitor (codenamed PD-0332991, trade name Ibrance) [2][17], including a phase 2 trial in patients with metastatic endometrial cancer (ClinicalTrials.gov Identifier: NCT02730429), underscoring the importance of identifying mechanisms of CDK4 activation in endometrial cancer.