Single-agent activity of the anti-GD2 antibody dinutuximab beta given as a long-term infusion in relapsed and refractory neuroblastoma (APN311-304)

10034 Background: Severe pain is a common side effect associated with short-term infusions of anti-GD 2 antibodies in combination with cytokines and isotretinoin and was reduced by the long-term infusison (LTI) strategy. We investigated efficacy and tolerability of a single-agent dinutuximab beta (DB)-LTI in patients with primary refractory or relapsed (R/R) stage 4 neuroblastoma (NB). Methods: Patients with R/R-NB were enrolled into an open label phase II trial. Previous anti-GD2 antibody therapies were allowed, if anti-DB antibody could not be detected. Patients received 5 cycles of DB-LTI (100 mg/m 2 /10 days). The primary endpoint was objective INRC response 24 weeks after the end of cycle 5. A sample size of 40 patients provides at least 80% power to reject the null hypothesis of an objective response in < 10% of patients if the true objective response rate observed was 25% (overall 1-sided significance level 0.05, exact binomial test). Secondary endpoints included safety, morphine use, best response and duration of response, pharmacodynamics and pharmacokinetics, 3-year progression-free (PFS) and overall survival (OS). Results: 40 patients were treated and 38 patients had evaluable response. The objective response rate 24 weeks after the end of cycle 5 was 26% (10/38) (CR/PR) (p = 0.0034) and 32% (12/38) (CR/PR/MR), with a higher response rate in refractory vs. relapsed patients (50% vs 25%; p = 0.0159). The best response rate was 53% (20/38). Of 14 patients with bone marrow involvement, 13 patients responded (93%) (12 CR, 1 PR). The median duration of response (CR/PR) was 238 days (95% CI [108-290d]). The 3-year probability of PFS was 31% (95% CI [0.17–0.47]) and of OS was 66% (95% CI [0.47–0.79]). Survival was higher for patients with refractory compared to relapsed disease (PFS 47% vs 19%, OS 93% vs 50%; p = 0.015). Grade 3 treatment emergent adverse events (TEAE) were pain (18%), diarrhea (5%), and hypokalemia (5%) and grade 3 hypotension, capillary leak and neurotoxicity were not observed. In patients who experienced pain, mean pain scores (scale 0–10, where 0 is no pain) were low and decreased between cycles 1 and 2: pain score at rest decreased from 1.01 to 0.30, and at stress from 1.45 to 0.28. There were no grade 4 or 5 TEAEs. The morphine usage decreased from cycle 2 to 5 (C2 95%; C3 12%; C4 0%; C5 0%). DB peak serum concentration in cycle 1 was 10.8±0.7 µg/ml and patients showed 7- and 11-fold increase of antibody-dependent cell-mediated (ADCC) and complement-dependent cytotoxicity (CDC), respectively. Anti-DB antibodies were found in 24% of patients. There was no association and no trend between exposure to DB (area under the curve, peak ot trough level) and response rate or survival in this cohort. Conclusions: Single-agent treatment with single agent dinutuximab beta given as long LTI without cytokines and without isotretinoin is effective and highly tolerable in R/R-NB. Clinical trial information: NCT02743429 .