People in this study will be placed into two groups. One group will take three medicines, and the other group will take two medicines and a fake pill. All pills are taken by mouth. At first, visits happen every week, then every month. Some visits may take a long time. The study has different parts and can last up to 5 years, depending on how well the treatment works.

This study is for people with advanced breast cancer that has not spread too far. Their cancer must have certain features: it responds to hormones, does not have HER2, and has a gene change called PIK3CA.

You may be able to join this study if you are an adult with advanced breast cancer that has certain features. Your cancer must respond to hormones, not have HER2, and have a gene change called PIK3CA. You must be able to take two cancer medicines and follow birth control rules. You cannot join if you are pregnant or breastfeeding.

This study is testing a new medicine called inavolisib to see if it works better than a fake pill when used with two other cancer medicines. Doctors want to know if this mix helps people with a certain kind of advanced breast cancer. They are also checking if the treatment is safe and how well people respond to it.