BACKGROUND:The impact of abbreviated neoadjuvant regimens for HER2+ breast cancer on rates of breast conservation therapy (BCT) is unclear. We aimed to determine BCT rates in a single-arm prospective trial of neoadjuvant paclitaxel/trastuzumab/pertuzumab (THP) in patients with stage II-III HER2+ breast cancer.
STUDY DESIGN:BCT eligibility was prospectively recorded before and after THP. Pre- and post-treatment mammogram and breast ultrasound were required; breast MRI was encouraged. Patients with a large tumor to breast size ratio were eligible for downsizing. Multifocal/multicentric tumors, extensive calcifications, and contraindications to radiation were considered BCT contraindications.
RESULTS:Overall, 92 patients who received neoadjuvant THP on trial were included. At presentation, 39 (42.4%) were considered eligible for BCT and 53 (57.6%) were not. BCT-eligible patients were older (median 54 years versus 47 years, respectively, p=0.006) and had smaller tumors by palpation (median 2.5 cm versus 3 cm, respectively, p=0.004). Of 53 BCT-ineligible patients, 28 were candidates for tumor downsizing, whereas 25 had contraindications to BCT. Overall, 51(55.4%) patients underwent BCT. Of the 28 patients who were candidates for downsizing, 22 (78.6%) became BCT-eligible after THP and 18/22 (81.8%) underwent BCT. In total, 44/92 (47.8%) patients experienced breast pathologic complete response (pCR, ypT0), including 11/25 (44.0%) patients with BCT contraindications at presentation.
CONCLUSIONS:De-escalated neoadjuvant systemic therapy led to high BCT rates in this cohort. The impact of de-escalated systemic therapy on local therapy and outcomes in early stage HER2+ breast cancer warrants further investigation.