TMB and BRAF mutation status are independent predictive factors in stage IIIC/D/IV melanoma patients receiving adjuvant PD-1 antibodies.

Abstract

9524 Background: High tumor mutational burden (TMB) is associated with a favorable outcome in metastatic melanoma patients treated with immune checkpoint inhibitors. However, data are limited in the adjuvant setting. As BRAF mutated patients have an alternative with targeted adjuvant therapy, it is important to identify predictive factors for relapse and recurrence-free survival (RFS) in patients receiving adjuvant PD-1 antibodies. Methods: We systematically evaluated all melanoma patients who started adjuvant PD-1 antibody therapy at our center between March 2018 and September 2019 to identify predictive factors for outcome. The median follow-up time from start of adjuvant anti-PD-1 therapy was 22 months. Tumor and normal tissue of all stage IIIC/D/IV patients and of stage IIIA/B patients with relapse were sequenced using a 700 genes panel. Predictive factors for relapse and RFS were identified using univariate and multivariate logistic and Cox regression analysis. RFS was estimated by the Kaplan-Meier method. TMB high was defined as the top 20 % of the cohort, corresponding to TMB values ≥ 20 Var/Mb. Results: A total of 165 patients were included in this study. According to AJCC 8th the initial tumor stages at the beginning of adjuvant anti-PD-1 therapy were as follows: N = 80 stage IIIA/B (48 %), N = 85 stage IIIC/D/IV (52 %). 72/165 patients (44 %) suffered a relapse, 44/72 (61 %) with loco regional and 28/72 (39 %) with distant metastases. Sequencing results were available from 79 / 85 patients with stage IIIC/D/IV. Here we present the results of this cohort. TMB low (OR 17.46, 95%CI 4.03-75.55; p < 0.0001) or absence of BRAF V600E/K mutation (OR 4.13, 95%CI 1.36-12.53; p = 0.012) were statistically significant, independent predictive factors for relapse. Also, with regard to RFS, BRAF mutation status and TMB were statistically significant and independent predictive factors. In the table below we display results for the combined variables. Patients with BRAF V600E/K mutation and TMB high had the best outcome. Conclusions: We identified TMB high as positive predictive marker in stage IIIC/D/IVmelanoma patients with adjuvant PD-1 antibody therapy. In tumors with BRAF V600E/K mutation and concurrent low TMB, adjuvant targeted therapy with BRAF- and MEK-inhibitors may be an alternative. This is also supported by the data on adjuvant dabrafenib and trametinib, which showed a greater advantage in patients with low TMB, presumably due to less tumor heterogeneity.[Table: see text]