Testing a combination of two medications after initial breast cancer treatment

This study is testing whether talazoparib works better when combined with atezolizumab (an immunotherapy drug) compared to talazoparib alone. All participants first receive standard initial treatment with palbociclib, an aromatase inhibitor, and a hormone injection. Then, about 4 weeks later, participants are randomly assigned to receive either talazoparib plus atezolizumab or talazoparib by itself.

Some breast cancers have specific genetic mutations that make them vulnerable to particular treatments. This trial is exploring whether combining this medication with an immunotherapy drug could help the immune system fight cancer more effectively than the medication alone.