Although the prognosis of HER2-positive breast cancer(BC)has been improving than before, that of locally advanced cases is not satisfactory. A 41-year-old female presented with a huge breast lump and massive lymphadenopathy, which was diagnosed as HER2-positive, unresectable, locally advanced BC. The first treatment, consisting of docetaxel, trastuzumab and pertuzumab, had only a limited and temporary effect, with subsequent mass regrowth. After initiation of the second treatment, trastuzumab emtansine(TDM1), the mass gradually shrank, and mastectomy and axillary lymphadenectomy were performed successfully. Histologically, several tiny invasive foci were observed in the mammary gland. No lymph node metastases were observed. The patient subsequently underwent radiation therapy and a 1-year course of TDM1 treatment. The patient has been in remission for 5 years. HER2-positive, locally advanced BC can be successfully treated with multimodal therapy, including anti-HER2 therapy, timely surgery and radiation therapy.