Efficacy and Safety of Trastuzumab Rezetecan Followed by CDK4/6 Inhibitors and Endocrine Therapy in HR+/HER2-Low/Ultra-Low Advanced Breast Cancer
This multicenter, prospective phase II clinical trial evaluates the efficacy and safety of sequential Trastuzumab rezetecan followed by dalpiciclib plus endocrine therapy (fulvestrant or aromatase inhibitors) in 45 patients with HR+/HER2-low/ultra-low advanced breast cancer. Enrolled patients will receive Trastuzumab rezetecan monotherapy for 6-8 cycles until clinical benefit, then transition to CDK4/6 inhibitors with endocrine therapy until disease progression or unacceptable toxicity. The primary endpoint is progression-free survival (PFS), with secondary endpoints including objective respon