A Phase I Study Of A Pd-L1 Antibody (Durvalumab) In Combination With Trastuzumab In Her-2 Positive Metastatic Breast Cancer (Mbc) Progressing On Prior Anti Her-2 Therapies (Cctg Ind.229)[Nct02649686]

1029Background: Immune checkpoint inhibitors are active in a broad range of advanced cancers. Antibody dependent cell mediated cytotoxicity is a mechanism of action of trastuzumab. The combination of the two may enhance activity and/or overcome acquired resistance. We performed a phase I study of durvalumab and trastuzumab in HER-2 positive MBC previously treated with chemotherapy and anti HER-2 antibodies to assess safety, efficacy and correlative end-points. Methods: Patients with HER-2 positive MBC, PS 0-2, and previously treated with taxanes and trastuzumab were enrolled on a standard 3+3 dose escalation schedule. Dose level 1 was standard doses of durvalumab (1125 mg i.v. day 1) and trastuzumab (8 mg/kg i.v. loading then 6 mg/kg day 1) on a q3 weekly cycle. An expansion cohort at the recommended phase II dose (RP2D) performed baseline and post cycle 1 tumor biopsies. The primary endpoint of the study was to establish the RP2D. Results: 15 patients were accrued across 3 Canadian centres from April – D...