This study aims to learn about a new medicine called PF-07248144, used with another drug called fulvestrant, for people with a specific type of breast cancer called HR-positive, HER2-negative. HR-positive means the cancer grows with hormones like estrogen. HER2-negative means the cancer has low levels of a protein that helps cells grow. This study is for people whose cancer worsened after a treatment called CDK 4/6 inhibitor therapy.

In this study, half of the participants will receive PF-07248144 with fulvestrant, while the other half will get their usual treatment, which can include medicines called everolimus, exemestane, or fulvestrant. PF-07248144 and other similar medicines are tablets that are taken at home daily in 28-day cycles. Fulvestrant is given as an injection at the clinic. The study compares the experiences to see if the new treatment is safe and works well.

• Participants must have advanced or metastatic breast cancer that did not improve with certain past treatments.
• The study involves daily tablets taken at home and clinic visits for injections.
• Participants' experiences will help determine the safety and effectiveness of the new treatment.