This study is investigating a new medicine, called PF-07248144, paired with a drug named fulvestrant to treat certain types of breast cancer. Breast cancer cells can have special proteins called receptors that attach to hormones like estrogen, helping the cancer grow. This study is for those whose breast cancer is HR-positive (meaning it has hormone receptors) and HER2-negative (meaning it has a low amount of a protein called HER2).

If you join, you might receive PF-07248144 as a pill every day, and fulvestrant through injections. The study will last in cycles of 28 days each. Some people will receive other treatments like everolimus or exemestane, which are also pills. This study aims to see if the new medicine combination is safe and helpful for people whose cancer has grown or worsened after previous treatment.

• The study requires daily medication and clinic visits for injections.
• It's for people whose cancer worsened after certain prior treatments.
• Participants will be split into different treatment groups for comparison.