A Study to Learn About the Study Medicine Called PF-07248144 in Combination With Fulvestrant in People With HR-positive, HER2-negative Advanced or Metastatic Breast Cancer Who Progressed After a Prior Line of Treatment.

This study is looking for adults aged 18 and over who have been diagnosed with HR-positive, HER2-negative breast cancer that has grown or spread and can't be removed by surgery or treated with radiotherapy to cure it.

To join, your breast cancer must have worsened after you've already had a specific type of hormone therapy called CDK4/6 inhibitor therapy. You might still be able to join if you've had other hormone treatments or if you've had certain gene changes treated. Your general health and how well you can perform daily activities will also be considered.

Some reasons you might not be able to join include having certain detectable changes in your tumour cells (like PIK3CA/AKT1/PTEN), having had more than two previous treatments for advanced cancer, or if you've had chemotherapy for advanced cancer. You also wouldn't be able to join if you have serious kidney, liver, or blood problems, or any other health condition that might make participating in the study risky.

If you join this study, you will either receive the new medicine PF-07248144 with fulvestrant, or a standard treatment (everolimus with either exemestane or fulvestrant). PF-07248144, everolimus, and exemestane are all tablets you would take at home every day. Fulvestrant is given as two injections into your buttocks during clinic visits.

Medicines are taken in 28-day cycles. You'll have regular visits to the study clinic for injections, check-ups, and to see how you're responding to the treatment. These visits will involve various assessments, which might include blood tests, scans, and physical examinations. The total duration of your participation in the study, including follow-up, will be explained by the study team.