Trastuzumab Deruxtecan in First-line HER2-positive Locally Advanced/MBC Patients Resistant to Trastuzumab+Pertuzumab

This is a national, multicenter single arm phase II clinical trial to study the efficacy, safety and tolerability of the administration of Trastuzumab Deruxtecan (T-DXd) in HER2-positive locally advanced or MBC patients resistant to trastuzumab plus pertuzumab plus taxane due to early relapse. Eligible patients will be enrolled and treated with T-DXd 5.4 mg/kg IV every 3 weeks. The T-DXd dose will be recalculated in the event that patients experience body weight variations greater than 10% during the treatment period. All patients enrolled will receive study therapy until radiographic or symptomatic progressive disease, unacceptable toxicity or withdraw of the informed consent, whatever occurs first. Study population: HER2-positive locally advanced or MBC patients who have not received prior chemotherapy or HER2 targeted therapy for advanced disease and with a Disease-Free Interval (DFI) of \<12 months from the end of prior (neo)adjuvant anti-HER2 therapy. Study Duration: The start date of the study is the date of the first site activation. Recruitment period will occur during approximately 24 months from the first patient in. The end date of the study is the date of the last visit of the last patient (LPLV), including follow-up. The duration of the study will be approximately 68 months from the first patient in. Performing exploratory objectives will be independent of the date of the end of the study.