A Study of Elacestrant Alone or in Combination With Abemaciclib in People With Endometrial Cancer

Inclusion Criteria: * Age ≥18 years at the time of informed consent. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Patients must have received previous platinum-based chemotherapy and treatment with a PD-1 inhibitor, together or separately, prior to enrolling on this trial. * Patients may have received no more than 1 prior line of chemotherapy for management of endometrial carcinoma. This includes platinum-based chemotherapy alone or combined with a PD-1 inhibitor, small molecule agents, and chemotherapy in combination with radiation therapy. A washout period of 14 days is required for chemotherapy °Adjuvant chemotherapy completed ≥ 12 months prior will not be counted toward prior therapy * Patients may have received ≤ one prior line of endocrine therapy for management of endometrial carcinoma. * No prior treatment with a CDK4/6 inhibitor * Measurable disease per RECIST v 1.1 criteria °Tumors within a previously irradiated field will be designated as "non-target" lesions unless progression is documented, or a biopsy is obtained to confirm persistence of tumor ≥ 90 days following completion of radiation therapy. * Advanced or recurrent endometrial carcinoma that is refractory to curative therapy. * Patients with the following histologic epithelial cell types are eligible: endometrioid adenocarcinoma, serous adenocarcinoma, undifferentiated carcinoma, de-differentiated, clear cell adenocarcinoma, mixed epithelial carcinoma, adenocarcinoma not ot…