This study is a Phase III non-inferiority trial targeting a specific subset of early breast cancer patients: those with HR-positive/HER2-negative, node-negative small tumors (typically ≤2cm) but who exhibit high-risk features for recurrence (such as high histological grade, high Ki-67 index, etc.). Currently, the standard adjuvant treatment for these patients often includes chemotherapy followed by endocrine therapy, despite their small tumor size, due to the high-risk biological characteristics. However, chemotherapy can bring significant toxicity and long-term side effects.
This trial explores whether a chemotherapy-sparing approach is feasible. It compares the efficacy and safety of using the CDK4/6 inhibitor Dalpiciclib combined with endocrine therapy (AI ± OFS) directly, without chemotherapy, against the traditional approach of chemotherapy (TC regimen) followed by endocrine therapy. The primary goal is to demonstrate that the chemotherapy-free regimen is not inferior to the chemotherapy-containing regimen in terms of 5-year invasive disease-free survival (iDFS). If successful, this study could potentially de-escalate treatment for this high-risk population, sparing them from chemotherapy-related toxicities while maintaining excellent oncological outcomes.