A Study on the Efficacy and Safety of Switching Between Two Targeted Strategies, HP+Chemotherapy and HPy+Chemotherapy, After Treatment Progression in HER-2 Positive Advanced or Metastatic Breast Cancer

This study adopts a multicenter, natural selection, observational design, and plans to enroll patients with HER-2 positive advanced or metastatic breast cancer treated at approximately 20 research centers nationwide. Patients with de novo stage IV disease or those with recurrent metastatic breast cancer who have not previously received trastuzumab, as well as patients with brain metastases, will be included for separate stratified efficacy analysis and will not be included in the overall analysis. The study plans to enroll effective data from 600 HER-2 positive advanced or metastatic breast cancer patients, who will be naturally allocated in a 1:1 ratio to either Group A (switching from HP + chemotherapy to HPy + chemotherapy) or Group B (switching from HPy + chemotherapy to HP + chemotherapy), with each group comprising approximately 300 patients. If first-line treatment fails, patients will switch to the alternative regimen in second-line treatment. All patients will continue treatment until disease progression, intolerable toxicity, or other reasons lead to discontinuation, with the number of treatment cycles recorded. The study is divided into three phases: screening/baseline period, treatment period (treatment period 1 + treatment period 2), and survival follow-up period. If patients develop intolerance to taxanes during treatment, clinicians may select alternative chemotherapy regimens such as vinorelbine, capecitabine, or eribulin based on clinical judgment. During the treatment period, patients will be followed up every two cycles, during which clinical data will be collected, including disease status assessments, laboratory tests, study drug usage, concomitant medications, and adverse events. After chemotherapy completion or treatment discontinuation, subsequent maintenance therapy, such as continued dual-targeted maintenance, may be administered by clinicians based on clinical needs until disease progression or intolerable toxicity occurs. Survival follow-