Abemaciclib and Letrozole in Treating Patients With Endometrial Cancer

This early phase I trial studies how well abemaciclib and letrozole work in treating patients with endometrial cancer and determines whether there are changes in patients' cancer cell biomarkers (a genetic feature or specific protein) for cell growth before and after treatment. Antihormone therapy with aromatase inhibitors, such as letrozole, may lessen the amount of estrogen made by the body. Abemaciclib blocks the activities of a class of proteins called cyclin-dependent kinase, which are involved in cell duplication. Giving letrozole and abemaciclib together may slow down cancer cell growth in patients with endometrial cancer.