Breast Cancer Clinical Trials

The purpose of this study is to determine the safety and efficacy of PF-07220060 with letrozole compared to approved treatments (ie, palbociclib, ribociclib or abemaciclib with letrozole) in people with breast cancer: * HR-positive (breast cancer cells that need estrogen or progesterone to grow) * HER2-negative (cells that have a small amount or none of a protein called HER2 on their surface); * locally advanced (that has spread from where it started to nearby tissue or lymph nodes) or metastatic disease (the spread of cancer to other places in the body) * who have not received any prior systemic anti-cancer treatment for advanced/metastatic disease. Approximately half of the participants will receive PF-07220060 plus letrozole while the other half of participants will receive the investigator's choice of treatment plus letrozole. The study team will monitor how each participant is doing with the study treatment during regular visits at the study clinic.