Materials and Methods: Retrospectively, data was collected from patients with HER2- positive early stage breast cancer who were receiving adjuvant trastuzumab. Then analysis of clinicopathological features of 88 patients and their treatment outcome was done. Results: 61 patients received trastuzumab and 27 patients didn't receive it. In patients who received trastuzumab (trastuzumab group), the median follow-up period was 24 months (8.0-40.0 months). Relapse-free survival (RFS) was 31.2 months (95% CI: 28.0-34.4) and overall survival (OS) was 34.9 months (95% CI: 32.3-37.5). The 3-year OS for all patients was 76.9% and RFS was 62.3%. In non-trastuzumab group: the median follow-up period was 26 months (8.0-40.0 months). They were followed up during the course of treatment and it was found that relapse-free survival (RFS) was 30.18 months (95% CI: 25.2-35.1) and overall survival (OS) was found to be 32.0 months (95% CI: 27.3-36.6). So, the 3-year OS for all patients was 59.8% and RFS was 48.3%. 13.1% of the patients in the trastuzumab group had an asymptomatic decrease in left ventricular ejection fraction by more than 10% which is discovered by the end of the treatment course. Data obtained from univariate analyses revealed that larger tumor size, positive nodal involvement, and positive estrogen receptor status were significantly associated (p<0.05) with RFS. Positive lymph node was identified as an independent prognostic factor with multivariate analyses of covariates displaying p<0.05 (HR=1.8, 95%CI 1.1 - 3, p=0.01).