CDK4/6 Inhibitor Intensification and Chemotherapy De-Escalation for Early-stage Luminal-HER2 Breast Cancer

For patients with hormone receptor-positive and HER2-positive breast cancer, the NCCN guidelines recommend that those with tumors larger than 1 cm or positive lymph nodes should receive standard adjuvant therapy comprising chemotherapy combined with targeted and endocrine therapy. In contrast, for patients with tumors smaller than 1 cm and negative lymph nodes, endocrine therapy alone or in combination with targeted therapy and chemotherapy may be considered. Therefore, in patients with stage I hormone receptor-positive and HER2-positive breast cancer, it remains unclear whether chemotherapy can be omitted by intensifying endocrine therapy through the addition of CDK4/6 inhibitors, particularly considering the intrinsic therapeutic efficacy of endocrine agents and their potential synergistic interaction with anti-HER2 therapy. To further minimize treatment-related toxicity and identify the optimal adjuvant treatment strategy for patients with HER2-positive stage I breast cancer, the investigators designed a phase III clinical trial involving hormone receptor-positive and HER2-positive stage I breast cancer patients. This trial aims to evaluate the efficacy and safety of a treatment regimen combining CDK4/6 inhibitors, endocrine therapy, and anti-HER2 therapy compared with the traditional approach of chemotherapy combined with anti-HER2 therapy.