This study checks if adding chemotherapy (ACT) to treatments called ovarian function suppression (OFS) and endocrine therapy (ET) helps people with a specific type of breast cancer live without cancer coming back. It's for younger women who haven't gone through menopause and have ER-positive (estrogen receptor-positive) and HER2-negative breast cancer. The study also looks at something called the recurrence score (RS), which helps predict cancer return.

• Study Length: Participation involves multiple visits over a period decided by the researchers.
• Eligibility: Women must be premenopausal and meet specific health criteria to join.
• Risks: Includes potential side effects from chemotherapy and other treatments.

Women under 35 are more at risk from breast cancer. Suppressing the ovaries is a treatment that's been around for a long time. But, as new treatments came in, its role became less clear. The study aims to find the best way to prevent cancer from coming back by comparing adding chemotherapy to just using OFS and ET. Participants need to meet certain health conditions, like having a specific kind of tumor and being in good general health. Pregnant women or those with other serious health issues can't join.