ESR1 and peritoneal carcinoma: In an effort to improve the efficacy of treatment in this setting, a randomized phase 2 trial of palbociclib (CDK4/6 inhibitor) in combination with letrozole versus placebo in combination with letrozole for patients with estrogen receptor (ER)-positive advanced or recurrent EC (NCT02730429) and a phase 2 trial of ribociclib (cyclin D1 and CDK4/6 inhibitor) and letrozole in ER-positive advanced ovarian, fallopian tube, primary peritoneal carcinomas and EC (NCT02657928) are currently recruiting patients.