Study Overview: This study looks at adding a new drug called Tersolisib to other cancer treatments for people with advanced breast cancer that has a specific genetic change called PIK3CA. The goal is to see if Tersolisib helps treat the cancer without causing bad side effects.

• Duration: The study continues as long as the drug helps and doesn't cause intolerable side effects.
• Visits: Participants may need to visit the study site regularly for monitoring.
• Eligibility: Participants must agree to use birth control and meet specific health criteria, such as having a PIK3CA mutation.

Key Terms: Hormone receptor-positive (HR+) means the cancer grows with hormones like estrogen. HER2-negative means the cancer doesn't grow from a protein called HER2. GnRH agonist is a drug that affects hormone levels. ASCO/CAP Guidelines are rules used to check cancer features.

Considerations: Participants cannot have certain health conditions like diabetes or active infections. It's important to be willing to follow the study's rules, including using birth control.