Many clinical trials has showed the superiority of combining trastuzumab to chemotherapy in the treatment of HER2 positive early breast cancer with tumor size ≥1cm or node metastasis.But in pT1n0m0 breast cancer patients, patients with HER2 positive tumor show worse prognosis than those with HER2 negative tumor.A short duration of trastuzumab administration contaminately with chemotherapy may have similar efficacy and lowerer toxiticy compared with standard one year therapy.Our study aims to study the efficacy and safety of 12 weeks adjuvant docetaxel plus trastuzumab in patients with tumors ≤1cm, node-negative, HER2-positive breast cancer.