Real-World 5-Year Outcomes of Patients Treated With the Adjuvant Paclitaxel Trastuzumab (APT) Regimen for Stage I HER2-Positive Early Breast Cancer: A Retrospective International Study.

Background: An anthracycline-free regimen of adjuvant paclitaxel and trastuzumab is the standard-of-care for patients with HER2-positive (HER2+) early breast cancer (eBC) with tumors ≤20 mm, node-negative tumors, based on the results of a single-arm phase II trial. We investigated the outcomes of this regimen in a real-world (RW) setting.

Methods: This retrospective, international RW study included patients with stage I HER2+ eBC treated with the APT regimen (tumors of 5-20 mm, node-negative (N0 or Nmi) and no previous history of BC). Data on demographics, tumor characteristics, treatments, and survival were extracted from medical records from 11 hospitals in Belgium, Italy, and Brazil. The primary endpoint was 5-year RW disease-free survival (rwDFS), and secondary was RW overall survival (rwOS).

Results: From January 2014 to July 2018, 252 patients were identified. The median age was 57.9 years, and 69.8% were postmenopausal women at diagnosis. Most tumors (88.1%) had ductal histology and were estrogen receptor-positive (81.7%). The median tumor size was 12 mm (Interquartile [IQR] 9.0-15.0). Breast-conserving surgery was performed in 77.8%, and radiotherapy was administered in 76.1% of patients. Median follow-up was 5.8 years (IQR 5.0-6.8). In total, 13 events were observed: 4 locoregional, 2 distant (1 bone and 1 visceral) and 7 second nonbreast primary malignancies. The 5-year rwDFS rate was 95.3% (95% Confidence Interval (CI) 92.7-98.1), and rwOS was 97.9% (95% CI 96.2-99.7).

Conclusion: Our RW data supports the effectiveness of the APT regimen, showing excellent 5-year survival outcomes in selected patients with low-risk HER2+ eBC.