The human epidermal growth factor receptor 2 (HER2) gene encodes a tyrosine kinase receptor that controls important signal transduction pathways in breast cancer. Amplification and overexpression of the HER2 gene occurs in approximately 20% of breast cancers and is associated with an aggressive clinical phenotype. Trastuzumab, a humanized monoclonal antibody that targets HER2 showed exceptional efficacy in the treatment of breast cancer. In the adjuvant treatment of breast cancer patients, five randomized trials showed significant benefit of trastuzumab, with a reduction in the rate of recurrence of approximately 50% and improvement in the rate of survival of approximately 30%. In the current study, positive early stage breast cancer samples treated with adjuvant trastuzumab provided by institute Jules Bordet (IJB) and KUL. Gene expression and clinical outcome data were available. to better understand the genetic regulations and effects of the trastuzumab, we profile the the genes expression of positive early stage breast cancer samples treated with adjuvant trastuzumab.