CDK4 and breast cancer: For patients with low HR expression (immunohistochemistry < 10%), the biological characteristics of the tumor are poor and close to those of HER2-positive and HR-negative breast cancer, which may not be suitable for the treatment of our case; Application of CDK4/6 inhibitor: CDK4/6 inhibitors are mainly used in the treatment of HER2-negative and HR-positive breast cancer, but there is currently limited evidence regarding their use in the treatment of HER2-positive and HR-positive breast cancer.