G1T48, an Oral SERD, Alone and in Combination With Palbociclib in ER-Positive, HER2-Negative Advanced Breast Cancer

This is a study to investigate the potential clinical benefit of G1T48 as an oral selective estrogen receptor degrader (SERD) alone and in combination with palbociclib, a cyclin dependent kinase 4/6 (CDK 4/6) inhibitor, in patients with estrogen receptor-positive, HER2-negative metastatic breast cancer. The study is an open-label design, consisting of 3 parts: dose-finding portion including food effect (Part 1), G1T48 monotherapy expansion portion (Part 2), and G1T48 in combination with palbociclib expansion portion (Part 3). All parts include 3 study phases: Screening Phase, Treatment Phase, and Survival Follow-up Phase. The Treatment Phase begins on the day of first dose with study treatment and completes at the Post-Treatment Visit. Approximately, 184 patients may be enrolled in the study.