Abstract P2-01-04: Real-world clinical outcomes of patients with stage I HER2-positive breast cancer treated with adjuvant paclitaxel and trastuzumab

Abstract Background: One year of adjuvant trastuzumab with 12 cycles of weekly paclitaxel represents the standard of care for patients with pathological tumor size ≤2cm, node-negative, HER2-positive early breast cancer. Data supporting this indication derive from a single-arm, phase II trial that enrolled 410 patients in the United States only, where the 3 years invasive disease-free survival (DFS) rate was 98.7% (95% CI 97.6-99.8). Therefore, real-world data regarding the clinical outcomes of these patients are needed to confirm the efficacy and safety of this adjuvant anthracycline-free regimen in this population. Methods: We conducted a retrospective, observational, multicentric study to investigate survival outcomes of patients with stage I HER2-positive early breast cancer treated with adjuvant paclitaxel and trastuzumab in seven selected sites in two countries (Belgium and Italy). Eligible patients were men and women with early breast cancer of pathological tumor size between 5 and 20 mm, node-negative (N0 or N1mic), and treated with weekly adjuvant paclitaxel for 12 weeks and trastuzumab (6 mg/kg every 3 weeks administration for 1 year). Patients with a history of previous cancers were not included. The primary endpoint was disease-free survival (DFS) at 3 years from diagnosis. Thus, an optimal follow-up of 3 years from surgery was required. Baseline clinico-pathological characteristics, treatment data, disease recurrences and survival status were extracted from medical records. Survival analysis was performed using log-rank regression test. Results: Overall, 240 patients who received their adjuvant treatment between January 2014 and December 2018 were included in the analysis. The median age was 59.5 years (IQR 50.0-66.9), and 69.6% of patients were post-menopausal at the time of diagnosis. Seventy (31.8%) patients had hypertension and 20 (8.3%) had other cardiac comorbidities. Ductal carcinoma was the most represented histological type (86.3%). The median tumor size was 12mm (IQR 9-15), only seven (2.9%) patients had N1miC, and the majority of tumors (85.0%) were ER-positive. Breast-conserving surgery was performed in 80.8% of patients and 78.2% of patients had adjuvant radiotherapy. The median number of administrated cycles of weekly paclitaxel was 12 (range 1-12) and for trastuzumab 18 (range 1-19). Only one patient stopped trastuzumab prematurely because of safety reason. Aromatase inhibitors were the most frequently administered endocrine therapy (75.7% of patients with ER-positive disease). With a median follow-up of 4.7 (IQR 3.6-5.6) years, we observed a 3-year DFS rate of 98.8% (95% CI 96.2-99.6), with only three disease recurrences (one local and two distant) and four deaths (none of which was breast cancer related) during the duration of the follow-up. Conclusions: In this real-world clinical outcome of patients with stage I HER2-positive breast cancer treated with adjuvant trastuzumab and paclitaxel appeared excellent, with a 1.2% rate of recurrence at 3 years. Our data support the efficacy of an anthracycline-free regimen in this population. A longer follow-up will provide more mature data on overall survival and late relapses, especially in the ER-positive subgroup of patients. Citation Format: Veronique Debien, Elisa Agostinetto, Marianna Sirico, Flavia Jacobs, Chiara Molinelli, Michel Moreau, Marianne Paesmans, Ugo De Giorgi, Armando Santoro, Donatienne Taylor, François P. Duhoux, Andrea Botticelli, Giacomo Barchiesi, Matteo Lambertini, Evandro de Azambuja, Martine Piccart. Real-world clinical outcomes of patients with stage I HER2-positive breast cancer treated with adjuvant paclitaxel and trastuzumab [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-01-04.