T-DM1 Combined With CDK4/6 Inhibitor Ribociclib

Inclusion Criteria: * Age ≥18 at the time of signing the informed consent. * Patient's ability to follow the study protocol as determined by the investigator. * A representative tumor tissue sample is required to confirm a HER2-positive diagnosis. HER2 expression status and ER expression status of invasive cancer lesions were determined based on previous pathological sections or current pre-treatment biopsy materials, and the HER2 IHC assay was locally confirmed to be consistent with 3+, or IHC assay with 2+, and further FISH detection was positive before study enrollment. * At least one evaluable lesion was detected by CT or MRI (see protocol for additional details). * For metastatic or recurrent breast cancer, there is currently no opportunity for surgical radical resection. * Metastatic or recurrent breast cancer that has received at least first-line rescue therapy in the past must have been treated with trastuzumab and taxanes. * The Physical status (ECOG) score of the Eastern Tumor Collaboration group was 0 or 1. * Sufficient haematology and organ function to meet the definition of laboratory test results, which must be provided within 14 days before the start of study therapy. * Fertile women should remain abstinent (no heterosexual intercourse) or use contraceptive methods. Exclusion Criteria: * Past treatment with other antibody-drug conjugate (ADC) drugs or anti-tumor therapy with CDK4/6 inhibitors. * Past treatment with other anti-HER2 drugs other than trastuzumab, pertuzumab and tyrosine kinase inhibitors (TKI). * Advanced breast cancer with central nervous system metastasis. * Patients who have developed other malignancies in the 5 years prior to screening, except adequately treated cervical cancer in situ, non-melanoma skin cancer, localized prostate cancer, ductal carcinoma in situ, or stage I uterine cancer. * Severe dysfunction of vital organs prior to enrollment (see protocol details). * Received an investigational drug within 28 days prior to initiation of study therapy. * Known hypersensitivity or hypersensitivity to CDK4/6 inhibitors. * The results of the serum pregnancy test were positive.