Phase 1a1b Study of the CDK4 Inhibitor BGB-43395 Alone or with Fulvestrant, Letrozole, or Elacestrant in People with Metastatic Hormone Receptor Positive, HER2-Negative Breast Cancer and Other Advanced Solid Tumors

What this Trial Is About

Researchers are evaluating BGB-43395, a selective CDK4 inhibitor, as a single treatment and in combination with fulvestrant, letrozole, or elacestrant for participants with hormone receptor positive HR and HER2-negative breast cancer as well as other advanced solid tumors. This phase 1a1b study aims to determine the recommended dosing of BGB-43395 while assessing safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity. The study has multiple parts Phase 1a involves dose escalation with increasing doses of BGB-43395 alone or combined with the other drugs to evaluate safety and tolerability. Selected dose levels then move to Phase 1a safety expansion cohorts with combinations in HRHER2- breast cancer. Phase 1b tests the recommended dose for expansion RFDE of BGB-43395 combined with fulvestrant or letrozole in HR breast cancer, including a subgroup receiving an anti-diarrheal agent to prevent side effects. Treatments are administered orally or by injection depending on the drug. Participants undergo regular monitoring for adverse events, dose tolerability, and response rates over up to approximately 60 months. Blood samples are taken to measure drug levels and metabolism during treatment cycles lasting 28 days. Researchers assess tumor response, disease control, and progression-free survival. The study also tracks safety events and collects pharmacokinetic data to guide dosing. Participation may last up to several years depending on treatment duration and follow-up assessments.

BGB-43395 Alone or as Part of Combination Therapies in Participants With Breast Cancer and Other Advanced Solid Tumors