A Phase 1/1b Study of PRT13722 in Participants With Advanced HR+/HER2- Breast Cancer

This is a first-in-human, open-label, multicenter, dose-escalation and dose-expansion study of PRT13722, a selective oral KAT6A protein degrader, in adults with locally advanced or metastatic HR-positive, HER2-negative breast cancer. The study will evaluate the safety, tolerability, dose-limiting toxicities, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of PRT13722 administered as monotherapy and in combination with fulvestrant, abemaciclib plus fulvestrant, or imlunestrant to determine recommended dose(s) for expansion and evaluate preliminary clinical activity. The study is conducted in three parts: Part 1: Monotherapy dose escalation and backfill cohorts. Part 2: Combination dose-escalation cohorts with fulvestrant, abemaciclib plus fulvestrant, and imlunestrant. Part 3: Combination dose-expansion cohorts to further evaluate safety and preliminary efficacy at the selected dose levels. Up to approximately 240 participants are planned for enrollment across the three parts of the study.