This study compares standard treatment that includes chemotherapy, hormone therapy, and ribociclib with a treatment that uses only hormone therapy and ribociclib. Researchers want to learn if chemotherapy is needed for all patients with this type of cancer.

People with breast cancer.

Participants may be able to join if they are adults who are postmenopausal women or men with a certain type of hormone sensitive, HER2 negative breast cancer. They must have had breast cancer surgery within the past 16 weeks. People with certain forms of noninvasive breast cancer may also be eligible.

This study is comparing the usual treatment of chemotherapy followed by hormone therapy and ribociclib with treatment using hormone therapy and ribociclib alone in postmenopausal women and men. Researchers want to learn if patients can be treated successfully without chemotherapy.