Circulating Tumor DNA Predicts Outcome from First-, but not Second-line Treatment and Identifies Melanoma Patients Who May Benefit from Combination Immunotherapy.

Purpose: We evaluated the predictive value of pretreatment ctDNA to inform therapeutic outcomes in patients with metastatic melanoma relative to type and line of treatment.
Experimental Design: Plasma circulating tumor DNA (ctDNA) was quantified in 125 samples collected from 110 patients prior to commencing treatment with immune checkpoint inhibitors (ICIs), as first- ( n = 32) or second-line ( n = 27) regimens, or prior to commencing first-line BRAF/MEK inhibitor therapy ( n = 66). An external validation cohort included 128 patients commencing ICI therapies in the first- ( N = 77) or second-line ( N = 51) settings.
Results: In the discovery cohort, low ctDNA (≤20 copies/mL) prior to commencing therapy predicted longer progression-free survival (PFS) in patients treated with first-line ICIs [HR, 0.20; 95% confidence interval (CI) 0.07-0.53; P < 0.0001], but not in the second-line setting. An independent cohort validated that ctDNA is predictive of PFS in the first-line setting (HR, 0.42; 95% CI, 0.22-0.83; P = 0.006), but not in the second-line ICI setting. Moreover, ctDNA prior to commencing ICI treatment was not predictive of PFS for patients pretreated with BRAF/MEK inhibitors in either the discovery or validation cohorts. Reduced PFS and overall survival were observed in patients with high ctDNA receiving anti-PD-1 monotherapy, relative to those treated with combination anti-CTLA-4/anti-PD-1 inhibitors.
Conclusions: Pretreatment ctDNA is a reliable indicator of patient outcome in the first-line ICI treatment setting, but not in the second-line ICI setting, especially in patients pretreated with BRAF/MEK inhibitors. Preliminary evidence indicated that treatment-naïve patients with high ctDNA may preferentially benefit from combined ICIs.
(©2020 American Association for Cancer Research.)