97 Background: Hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-positive tumors generally cluster within the luminal/HER2 subset; whereas HR-negative/HER2-positive tumors reside in HER2-enriched subset. We investigated whether the efficacy of HER2-targeted therapy for HER2-positive tumors differs by HR status. Methods: Sixty-eight patients with operable breast cancer received trastuzumab plus taxane based therapy before surgery at Keio University Hospital from March 2009 to April 2012. All tumors were HER2-positive by immunohistochemistry (IHC) or fluorescence in situ hybridization. Expressions of ER, PgR, and Ki67 were performed by IHC in core needle biopsy samples at baseline. Pathological complete response (pCR) defined as no invasive residuals in breast. All patients with luminal/HER2 tumors received adjuvant endocrine therapy in addition to adjuvant trastuzumab monothereapy. Results: Sixty-eight patients with HER2-positive tumors were divided into 35 (51.5%) patients with luminal/HER2 tumors and 33(48.5%) patients with HER2-enriched tumors, respectively. There were no significant differences in tumor size, clinical nodal status, nuclear grade, and Ki67 status between the two groups. Clinical complete response rate and objective response rate were similar between the two groups. Patients with luminal/HER2 tumors were significantly younger than patients with HER2-enriched tumors (median age (range): 53 (35-78) vs. 61 (31-72), p=0.041). Compared to patients with luminal/HER2 tumors, patients with HER2-enriched tumors had significantly higher pCR rate (28.6% vs. 69.7%, p=0.002). With 24 months median follow-up, no significant differences were observed between the two groups with respect to disease-free survival. Estimated 2-year disease-free survival for luminal/HER2 and HER2-enriched was 94.3% and 97.0%, respectively (p=1.000). Conclusions: HER2-enriched breast cancer showed significantly higher pCR rate to HER2-targeted therapy compared with luminal/HER2 breast cancer. However, there was no significant difference in disease-free survival between the two groups.