• Anna Weiss, Tianyu Li, Neelam V Desai, Nadine M Tung, Philip D Poorvu, Ann H Partridge, Faina Nakhlis, Laura Dominici, Natalie Sinclair, Laura M Spring, Meredith Faggen, Michael Constantine, Ian E Krop, Michelle DeMeo, Eileen Wrabel, Jillian Alberti, Sona Chikarmane, Nabihah Tayob, Tari A King, Sara M Tolaney, Eric P Winer, Elizabeth A Mittendorf, and Adrienne G Waks.
• From the Harvard Medical School, Boston MA (Weiss, Li, Desai, Tung, Poorvu, Partridge, Nakhlis, Dominici, Sinclair, Spring, Faggen, Constantine, Krop, Chikarmane, Tayob, Fing, Tolaney, Winer, Mittendorf, Waks).
• J. Am. Coll. Surg. 2023 Aug 1; 237 (2): 247256247-256.

BackgroundThe 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 or III HER2+ breast cancer.Study DesignBCT eligibility was prospectively recorded before and after THP. Pre- and posttreatment 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.ResultsOverall, 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 vs 47 years, respectively; p = 0.006) and had smaller tumors by palpation (median 2.5 vs 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 of 22 (81.8%) underwent BCT. In total, 44 of 92 (47.8%) patients experienced breast pathologic complete response (ypT0), including 11 of 25 (44.0%) patients with BCT contraindications at presentation.ConclusionsDe-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.Copyright © 2023 by the American College of Surgeons. Published by Wolters Kluwer Health, Inc. All rights reserved.

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