An Interventional Safety and Efficacy Phase 1b/2, Open-Label Study to Investigate Tolerability, PK, and Antitumor Activity of Vepdegestrant (ARV-471/PF-07850327), an Oral Proteolysis Targeting Chimera, in Combination with PF-07220060 in Participants Aged 18 Years and Older with ER+/HER2- Advanced or Metastatic Breast Cancer [Advarra]

The purpose of this study is to learn about the safety and effects of giving vepdegestrant along with PF-07220060. Vepdegestrant is studied to see if it can be a possible treatment for advanced metastatic breast cancer. This type of cancer would have spread from where it started (breast) to other parts of the body and would be tough to treat. The study is seeking for participants who have breast cancer that:

• is hard to treat (advanced) and may have spread to other organs (metastatic).
• is sensitive to hormonal therapy (it is called estrogen receptor positive).
• is no longer responding to treatments taken before starting this study.

All the participants will receive vepdegestrant and PF-07220060. Both medicines will be taken by mouth. The medicines will be taken at home. The experience of people receiving the study medicines will be studied. This will help see if the study medicines are safe and effective. Participants will continue to take vepdegestrant and PF-07220060 until:

• their cancer is no longer responding, or
• side effects become too severe. They will have visits at the study clinic about every 4 weeks.