Abstract
PURPOSE: Studies have demonstrated an association between quantity of circulating tumor DNA (ctDNA) and poorer survival. We investigated the relationship between percent ctDNA (%ctDNA), total number of ctDNA alterations, and overall survival (OS) in liquid biopsies. MATERIALS AND METHODS: Overall, 418 patients with blood-based next-generation sequencing (54 to 73 genes) were analyzed. Eligible patients included those who had advanced/metastatic solid tumor malignancies and never received immunotherapy treatment, which may alter the survival curve in patients with high mutational burden. RESULTS: Patients with a high (≥ 5%) %ctDNA had significantly shorter OS versus those with intermediate (≥ 0.4% to < 5%) or low (< 0.4%) values (median OS, 7.0 v 14.1 v not reached [NR] months, respectively; P < .0001). Patients with a high (≥ 5) total number of alterations had significantly shorter OS versus those with intermediate (≥ 1.46 to < 5), low (< 1.46), or no alterations (median OS, 4.6 v 11.7 v 21.3 v NR months, respectively; P < .0001). The total number of alterations correlated with %ctDNA (r = 0.85; 95% CI, 0.81 to 0.87; P < .0001). However, only an intermediate to high total number of alterations (≥ 1.46) was an independent predictor of worse OS (hazard ratio, 1.96; 95% CI, 1.30 to 2.96; P = .0014; multivariate analysis). CONCLUSION: We demonstrate that the total number of alterations and %ctDNA have prognostic value and correlate with one another, but only the total number of alterations was independently associated with survival outcomes. Our findings suggest that the total number of alterations in plasma may be an indicator of more aggressive tumor biology and therefore poorer survival.