Abstract 2650: In depth immune profiling of the response of melanoma to MAPK inhibition

Abstract Melanoma patients with clinically palpable regional lymph node metastases (AJCC Stage III) carry a risk of relapse and death that approaches 70% at 5 years. The NeoCombi study is a pilot phase II study of neoadjuvant dabrafenib plus trametinib in patients with resectable Stage IIIB-C BRAFV600 mutation positive melanoma. Patients receive 12 weeks of combined drug treatment, followed by surgical resection of all disease. Patients then continue combination drug treatment for a further 40 weeks. We aimed to identify host and tumour biomarkers that predict response to MAPK inhibition. Blood and tumour samples were obtained at baseline, early during treatment (3-7 days on therapy), at completion resection after 12 weeks on therapy, and, if relevant, on progression. Additional blood samples were also collected every 2 weeks up to 12 weeks of therapy. Samples were processed to generate plasma, peripheral blood mononuclear cells (PBMCs), fresh frozen tumour and where possible, tumour-dissociates and cell lines (tumour and immune cells). We have profiled tumour-specific and peripheral immune responses using a combination of flow cytometry, mass cytometry and multiplex cytokine/chemokine arrays. We also profiled circulating tumour-associated DNA (ctDNA) in plasma. To date, we have accrued 17 patients onto the NeoCombi study. Primary analysis of the first 12 patients has been completed. Decreases in ctDNA and tumour viability, in addition to immunophenotype changes, were seen within 1 week of starting treatment. Changes in immunophenotype continued throughout the first 12 weeks of treatment with conversion of CD8+ and CD4+ naive (CD45RA+) cells to effector cells (CD45RA-) in most patients. We also noted that activation of regulatory T cells (CD4+CD25+CD127-HLA-DR+) increased over the first 12 weeks of treatment in patients with partial pathological responses compared to those with complete pathological responses. Interestingly, the cytokine profile remained relatively stable across treatment within each patient, suggesting that factors already present at baseline may determine response to treatment. A pro-inflammatory cytokine signature has been identified as a potential biomarker of patients likely to relapse and in vitro validation studies are currently underway. Additionally, although ctDNA was only detectable in 42% of patients (compared to over 70% in patients with stage IV disease), high levels of ctDNA identified patients at highest risk of relapse and, if detectable, proved a useful marker to monitor treatment response. In conclusion, we have identified both host and tumour-specific biomarkers which may be useful to predict (and to monitor) response to MAPK inhibition in melanoma patients. Citation Format: Sarah J. Welsh, Suzanah Boyd, Helen McGuire, Maria Gonzales, Alexander M. Menzies, Hojabr Kakavand, Elisa James, Elizabeth Smith, Barbara Fazekas, Richard F. Kefford, Alex Guminski, Richard A. Scolyer, Georgina V. Long, Helen Rizos. In depth immune profiling of the response of melanoma to MAPK inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2650.