This clinical trial is focused on studying advanced breast cancer, specifically in cases where the cancer is hormone receptor-positive and HER2-negative. These types of breast cancer have shown resistance to certain treatments, such as CDK4/6 inhibitors and aromatase inhibitors. The study will explore a new treatment combination using two medications: M1774, which is an ATR inhibitor, and fulvestrant, a solution for injection. The purpose of the study is to evaluate the safety and effectiveness of this combination in patients whose cancer has specific genetic changes that may affect how the cancer grows.
Participants in the study will receive the treatment over a period of up to 18 months. The study will be conducted in two phases. The first phase aims to find the best dose of M1774 when used with fulvestrant. The second phase will further assess the safety and potential benefits of this treatment combination. Some participants may receive a placebo as part of the study to help compare the effects of the new treatment.
The study will monitor participants for any side effects and measure how well the treatment works in controlling the cancer. This includes looking at how long participants live without the cancer getting worse. The study will also collect information on how the body processes the medications. The trial is expected to continue until 2028, with recruitment starting in 2024.



France