This study is looking at how well a drug called **ribociclib**, combined with regular hormone therapy (**endocrine therapy** or ET), works for people with a type of early breast cancer that is **HR-positive** (hormone receptor positive) and **HER2-negative** (a protein that does not promote cancer growth). The study includes three parts: screening, treatment, and follow-up. During the treatment phase, participants will take ribociclib pills once a day for 21 days, then take a break for 7 days. This cycle will repeat for about 3 years. Participants will continue their regular hormone therapy each day. After finishing treatment, there will be follow-up visits until about 4 years after treatment starts.

• The study lasts around 3 years of treatment with follow-up visits after.
• Participants must have early-stage breast cancer and cannot be pregnant.
• There are no added costs for study medications.

It's important to check with your doctor to see if this study is right for you and to understand any risks involved.