Background: The poor prognosis of glioblastoma (GBM; WHO grade IV) results from a high rate of disease recurrence and lack of effective treatment options. Depatuxizumab mafodotin (depatux-m, ABT-414) is comprised of an EGFR-directed antibody, depatuxizumab (depatux, ABT-806), conjugated to the microtubule toxin monomethyl auristatin F (MMAF, mafodotin). Once bounded with tumor cells, depatux-m is internalized and releases the cytotoxin, resulting in cell death. Here, we report safety, pharmacokinetic (PK) and efficacy in an ongoing phase 1/2 study of Japanese patients with/without EGFR-amplified recurrent GBM (rGBM).Methods: M13-714 (INTELLANCE-J, NCT02590263) is a non-randomized, phase 1/2 study in Japanese patients. Phase 1 assessed tolerability and PK where the dose escalation of depatux-m was from 0.5 to 1.25 mg/kg/Q2W at day 1 and 15 during 28-day cycle until progression disease (PD) or intolerable toxicity. Phase 2 assessed efficacy and safety of depatux-m in EGFR-amplified, rGBM and patients received 1.0 mg/kg of depatux-m on day 1 and 15 + 150 mg/m² temozolomide (TMZ) on days 1-5 during each 28-day cycle until PD or intolerable toxicity. Results: As of 10 Jan 2019, 38 patients (WHO grade ≥3) were enrolled (9 in phase 1, 29 in phase 2). There was no dose limiting toxicity in phase 1. The recommended phase 2 dose was 1.25 mg/kg where the most common adverse events (AEs) were punctate keratitis in 21 patients (72%); lymphopenia in 14 patients (45%), thrombocytopenia in 13 patients (41%). Grade 3/4 AEs included thrombocytopenia and lymphopenia in 20 patients (69%). Ocular AEs were reported in 27 patients (93%) including punctate keratitis (72%). PK results (31 patients) in both phases were similar to those of non-Japanese result. Progression Free Survival (PFS) of 27 patients in phase 2 for 12 and 6 months were 8% and 27.5% respectively. The median PFS was 4 months. The overall survival (OS) for 24, 12 and 6 months were 28%, 62.5% and 93% respectively. The median OS was 15.5 months. Conclusions: Preliminary safety, PK and efficacy in Japanese patients with/without EGFR-amplified, rGBM suggests depatux-m was tolerated and showed encouraging anti-GBM effects. Clinical trial information: NCT02590263