Circulating Tumor Cells and Treatment De-escalation After Neoadjuvant Therapy for HER2 Positive Breast Cancer

Patients with HER2 positive breast cancer (hormone receptors positive or negative), which are candidate to neoadjuvant therapy with pertuzumab and trastuzumab will be included. Blood samples will be collected at baseline (before neoadjuvant start) for the analysis of CTCs and its positivity for HER2 by IHC and ISH. Patients with pathological complete response will be included in the randomization phase of the study. There will be 2 cohorts: HER2 positive CTCs at baseline and HER2 negative/absent CTCs at baseline. In each cohort, patients will be randomized in 1:1 ratio for adjuvant trastuzumab versus adjuvant trastuzumab + pertuzumab