351P - Impact of pertuzumab and T-DM1 on prognosis of HER2-positive metastatic breast cancer (MBC) and factors affecting their efficacy: Results from the AGMT_MBC-registry

Both pertuzumab and T-DM1 improved overall survival (OS) of HER2+ metastatic breast cancer (MBC) in clinical trials. Little is known about their activity outside of clinical trials and when administered sequentially or after (neo)adjuvant pretreatment. Here we present real-word data from the MBC-Registry of the Austrian Study Group of Medical Tumor Therapy (AGMT). The AGMT-MBC-Registry is a multicenter nationwide ongoing retrospective and prospective registry for MBC patients in Austria. Unadjusted, univariate survival probabilities of PFS and OS were calculated by the Kaplan-Meier method and compared by the log-rank test, multivariate hazard ratios (HR) were estimated by Cox regression models. In this analysis patients with known HER2 status and available survival data who received at least one palliative treatment line were included. As of 31/01/2019, 1262 patients were included in the AGMT-MBC-Registry. Out of 1090 evaluable patients, 256 (23.5%) were HER2+. Compared to patients with HER2- disease, HER2 positivity was significantly associated with longer OS (median OS 42.7 vs. 33.6 months; HR 0.80; 95%CI 0.67-0.96; P=0.017). Patients treated with pertuzumab (106/256=41.4%) or T-DM1 (49/256=19.1%) had a significantly longer OS than patients who were not treated with these agents, respectively (HR 0.35; 95%CI 0.24-0.52; P