Abstract PS3-11-16: Choice in HER2-positive locally Advanced breast cancer of Neoadjuvant Taxane: a retrospective review of practice

Abstract Background: The NeoSphere trial first established docetaxel-based dual HER2 blockade with pertuzumab and trastuzumab as an effective neoadjuvant regimen, yielding superior pathologic complete response (pCR) rates, though without conclusive long-term survival benefit. The subsequent PEONY trial confirmed the pCR advantage and demonstrated improved 5-year event-free survival with this regimen. Despite this, paclitaxel—administered weekly (P1) or every 3 weeks (P3)—is commonly used in clinical practice due to its more favorable tolerability profile. Whether the choice of taxane impacts efficacy or toxicity in the context of modern dual HER2-targeted therapy remains unclear, particularly in Canada, where pertuzumab reimbursement has been variable. Methods: We conducted a single-center retrospective cohort study at the Jewish General Hospital in Montreal, Quebec, Canada. Eligible patients were adults with HER2-positive stage II-III breast cancer who received at least one dose of pertuzumab and trastuzumab between December 2021 and December 2024, and underwent complete (R0) surgical resection. Patients were grouped by neoadjuvant taxane: docetaxel 75-100 mg/m2 every 3 weeks (D3), paclitaxel 175 mg/m2 every 3 weeks (P3), or paclitaxel 80 mg/m2 weekly (P1). The primary endpoint was pCR; the secondary endpoint was the highest CTCAE v5.0 grade of adverse events. Fisher’s exact test was used to calculate odds ratios for pCR, and the Mann-Whitney U test compared toxicity grade distributions. Prism 10.5 was used in the analysis. Results: Cohort: We identified 87 patients: 60 received paclitaxel (45 weekly, 15 every 3 weeks) and 27 received docetaxel. The median age was 55 years (range 25-83) and median clinical stage was IIB (range IIA-IIIC); these were balanced between taxane cohorts (P = 0.37 and P = 0.59, respectively). Estrogen receptor status was similarly distributed (P = 0.48). Efficacy: Paclitaxel either every 3 or 1 week showed similar efficacy to Docetaxel every 3 weeks (P = 0.35), with a slight trend in our data towards better response with Paclitaxel. Safety: Paclitaxel either every 3 or 1 week and docetaxel every 3 weeks yielded safety profiles as measured by adverse events (CTCAE v5), P = 0.68 for paclitaxel every 3 weeks versus docetaxel, and P = 0.60 when comparing docetaxel against paclitaxel every 3 weeks and every 1 week. Conclusion: In routine clinical practice, paclitaxel—whether weekly or q3-weekly—achieves comparable pCR rates and acute toxicity to docetaxel when combined with pertuzumab and trastuzumab. Given paclitaxel’s logistical and tolerability advantages, these data support its use as an alternative taxane backbone in HER2-positive neoadjuvant therapy. Prospective randomized studies with survival endpoints are warranted. Adjustment for confounders will be addressed in future analyses. Citation Format: R. Barros, B. Jiao, A. Lozano, A. Shah, E. Bushatsky Andrade de Alencar, M. Frija-Gruman, J. Cools-Lartigue, N. Gagnon-Choy, I. Prakash, K. Ma. Choice in HER2-positive locally Advanced breast cancer of Neoadjuvant Taxane: a retrospective review of practice [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-11-16.