Outcomes of trastuzumab therapy in HER2-positive early breast cancer patients

Background Previous large trials with trastuzumab (TZM) showed improved outcome in patients with HER2-positive early-stage breast cancer. However, the efficacy and safety of TZM in Japanese patients have not been fully evaluated. We have therefore conducted an observational study in Japan. Methods This was a retrospective and a prospective observational study in which data on women with histologically confirmed HER2-positive invasive breast cancer who received TZM for stage I–IIIC disease were collected from 56 institutions that participated in the Japan Breast Cancer Research Group and the efficacy of each treatment regimen analyzed. Results A total of 2,024 patients treated between July 2009 and June 2011 were initially enrolled in this study; in August 2013, the patient cohort comprised 2,009 patients. Of these, 142 (7.5 %) were aged ≥70 years, 1,097 (58.1 %) had clinically node-negative (cN0) breast cancer, and 883 (47.4 %) were estrogen receptor-positive. Treatment options were neoadjuvant therapy (662 patients) and adjuvant therapy with TZM (1,228 patients). Three-year overall survival (OS) rates in the entire cohort and in the neoadjuvant and adjuvant cohorts, respectively, were 98.9 [95 % confidence interval (CI) 98.2–99.3], 98.3 (95 % CI 96.8–99.1 %), and 99.2 % (95 % CI 98.4–99.6), respectively. Three-year disease-free survival (DFS) rates in the entire cohort and in the neoadjuvant and adjuvant cohorts, respectively were 94.2 (95 % CI 93.0–95.2), 94.8 (95 % CI 93.0–95.9), and 93.1 (95 % CI 90.7–94.9 %), respectively. Multivariate analysis showed that age and nodal status negatively correlated with DFS. Age was the only factor which correlated with OS rate. Adverse events (AEs) associated with TZM and grade 3/4 AEs were reported in 356 (18.8 %) and 14 (0.6 %) patients, respectively. Grade 3/4 cardiac toxicities were reported in 11 patients. Conclusion Based on data from our patient cohort of Japanese women with HER2-positive early-stage breast cancer, the efficacy and safety of systemic therapy with TZM are comparable to data from previously conducted large trials. Progress in anti-HER2 therapy for patients aged ≥70 years who have a poorer prognosis is needed.