Chemotherapy-Free pCR-Guided Strategy With Trastuzumab-pertuzumab and T-DM1 in HER2-positive Early Breast Cancer

Patients ≥ 18 years of age with previously untreated HER2 IHC 3+ invasive carcinoma according to ASCO/CAP 2018 guidelines. Tumor size between \>5 to 30 mm by breast MRI and node-negative status by clinical exam, MRI, and ultrasound. In patients with suspected axillary node involvement, a negative fine needle aspiration biopsy (FNAB) will be mandatory. Central review for: Breast MRI. HER2 status. Neoadjuvant treatment will consist In 8 cycles of fixed-dose subcutaneous (SC FDC) HP combination (± ET according to HR status). urgery will be performed within 4 weeks from the last cycle of HP (sentinel node biopsy will be mandatory; subsequent axillary dissection will be performed according to local guidelines). Surgery will require free margins for any infiltrating or DCIS lesion. Radiotherapy will be mandatory for patients with breast preservation. Adjuvant systemic therapy will be started within 4 weeks from surgery depending on pathological report: Arm A: pCR (breast and axilla): HP SC FDC x 10 cycles. Arm B: Residual invasive breast tumor and/or ypN0(i+), ypN0(mol+), ypN1mi: T-DM1 x 10 cycles Arm C: ypN1 to N3: T-DM1 x 10 cycles, with physician's choice chemotherapy allowed between surgery and T-DM1. All patients with HR\[+\] tumors will receive adjuvant ET up to at least 5 years (ET will also be administered in association with adjuvant HP or T-DM1, with the exception of the cycles involving the use of chemotherapy in Arm C).