Thus, adding one year of adjuvant trastuzumab to chemotherapy treatment for HER2+ early-stage breast cancer patients is not cost-effective in Vietnam as the ICERs of 519 million VND per QALY gained exceed the cost-effective threshold of 1-time GDP per capita and the threshold of 3-time GDP per capita by 6.3 times and 2.1 times, correspondingly. This evidence concerns the gene ERBB2 and breast cancer.