e12080 Background: Evaluation of the histological response after neoadjuvant chemotherapy with Docetaxel-carboplatin and bio similar Trastuzumab (CANMAB 150mg) in Her2 positive breast cancer. The primary end point was pathologic complete response (pCR) rate, determined from surgical specimens. Methods: Between March 2017 and June 2018, we treated 39 patients with Her2-positive breast cancer satge II (61,5%), III (38,5%), with a neoadjuvant schedule of docetaxel (75 mg/m2), carboplatin (AUC 6) and biosimilar trastuzumab (CANMAB 150mg: 8 mg/kg loading dose then 6 mg/kg) every 3 weeks. Patients were diagnosed at a mean age of 48 years; 52,28% had hormone receptor-positive tumors and 87,17% of patients were node positive. All pts received 6 cycles of chemotherapy followed by surgery and one year of biosimilar trastuzumab. Results: We report the preliminary results of a prospective study on the use of the biosimilar trastuzumab combined with preoperative chemotherapy in Her2 positive breast cancer. Thirty nine patients (100%) completed six cycles of therapy. Surgery was breast conservative in 6 (15,38%) of 39 patients. Fifteen of the Thirty one patients (48%) achieved a pCR, Twelve of the twenty six node-positive patients (46,15%) experienced nodal conversion. There was a significantly lower response in HR-positive patients compared to HR-negative ones (26,7 vs 73,33%). No case of congestive heart failure was observed. Conclusions: The use of biosimilar trastuzumab with docetaxel and carboplatin achieved promising efficacy, with a good pCR rate (48%) in stage II or III Her2-positive breast cancer.