Abemaciclib for Molecular Residual Disease Detected by Circulating Tumor DNA in HR+/HER2- Early Breast Cancer

The goal of this clinical study is to determine whether monitoring ctDNA and treating patients who become ctDNA-positive with abemaciclib can help prevent the recurrence of hormone receptor-positive, HER2-negative breast cancer after curative surgery and standard therapy. The study will also assess the safety of abemaciclib and the medical problems that may occur during treatment. Participants will receive routine follow-up after surgery, undergo regular blood tests to measure ctDNA, and, if ctDNA becomes positive, receive abemaciclib for a defined treatment period with scheduled clinic visits for examinations and safety assessments. Researchers will evaluate recurrence-free survival, distant recurrence-free survival, adverse events, the time between ctDNA positivity and clinical recurrence, and the rate of ctDNA clearance at the end of abemaciclib therapy.