Neoadjuvant ipilimumab + nivolumab (IPI+NIVO) in palpable stage III melanoma: Updated data from the OpACIN trial and first immunological analyses

9586 Background: The combination of IPI+NIVO induces high response rates and improved overall survival in late stage melanoma. T cell checkpoint inhibition is of greatest value at the moment of TCR triggering and therefore dependent on the amount of antigen present, indicating that adjuvant immunotherapy may work most efficiently, when initiated prior to surgery. Methods: Two-arm Phase 1b feasibility trial of 20 high risk AJCC stage IIIB and IIIC melanoma patients with palpable nodal disease receiving the combination of IPI 3mg/kg and NIVO 1mg/kg, either adjuvant four courses after surgery, or split two courses neo-adjuvant and two courses adjuvant. Results: In this update all 20 patients are evaluable. Neo-adjuvant application of IPI+NIVO was feasible and no surgery-associated adverse events were attributed to (neo-)adjuvant therapy. 18/20 patients had to stop early due to grade 3/4 toxicities. Neo-adjuvant IPI+NIVO reduced tumor load in 8/10 patients (3 pCR, 4 near-pCRs [minimal remaining micrometastases], 1 pPR [75% reduction], 1 SD and 1 PD). To date, after a median follow-up of 45 weeks (range 13-74), none of the responders in the neoadjuvant arm has relapsed. Relapse was observed for both non-responders within the neo-adjuvant arm and for 3 patients within the adjuvant arm. TCR sequencing and MHC tetramer-based analysis to compare the induction and expansion of tumor (neo-)antigen-specific T cell responses between both treatment arms are underway and will be presented. Conclusions: The combination of IPI+NIVO in the (neo-)adjuvant treatment setting for high risk stage III melanoma patients is feasible and induces very frequent responses. At the same time, severe grade 3/4 toxicity is more frequent than expected from stage IV melanoma patient study data. These results indicate that IPI+NIVO is a promising combination for neo-adjuvant treatment in stage III melanoma. Adjusted combination schemes are currently tested in the phase 2 OpACIN-neo trial, with the aim of reducing toxicity while preserving efficacy. Clinical trial information: NCT02437279.