Multianalyte Prognostic Signature Including Circulating Tumor DNA and Circulating Tumor Cells in Patients With Advanced Pancreatic Adenocarcinoma

Abstract

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is associated with a poor prognosis. Multianalyte signatures, including liquid biopsy and traditional clinical variables, have shown promise for improving prognostication in other solid tumors but have not yet been rigorously assessed for PDAC.

Materials and methods: We performed a prospective cohort study of patients with newly diagnosed locally advanced pancreatic cancer (LAPC) or metastatic PDAC (mPDAC) who were planned to undergo systemic therapy. We collected peripheral blood before systemic therapy and assessed circulating tumor cells (CTCs), cell-free DNA concentration (cfDNA), and circulating tumor KRAS (ctKRAS)-variant allele fraction (VAF). Association of variables with overall survival (OS) was assessed in univariate and multivariate survival analysis, and comparisons were made between models containing liquid biopsy variables combined with traditional clinical prognostic variables versus models containing traditional clinical prognostic variables alone.

Results: One hundred four patients, 40 with LAPC and 64 with mPDAC, were enrolled. CTCs, cfDNA concentration, and ctKRAS VAF were all significantly higher in patients with mPDAC than patients with LAPC. ctKRAS VAF (cube root; 0.05 unit increments; hazard ratio, 1.11; 95% CI, 1.03 to 1.21; P = .01), and CTCs ≥ 1/mL (hazard ratio, 2.22; 95% CI, 1.34 to 3.69; P = .002) were significantly associated with worse OS in multivariate analysis while cfDNA concentration was not. A model selected by backward selection containing traditional clinical variables plus liquid biopsy variables had better discrimination of OS compared with a model containing traditional clinical variables alone (optimism-corrected Harrell's C-statistic 0.725 v 0.681).

Conclusion: A multianalyte prognostic signature containing CTCs, ctKRAS, and cfDNA concentration outperformed a model containing traditional clinical variables alone suggesting that CTCs, ctKRAS, and cfDNA provide prognostic information complementary to traditional clinical variables in advanced PDAC.

FIG 1.

Box plots demonstrating distribution of (A) cfDNA concentration (ng/mL); (B) ctKRAS mutation variant allele frequency (ctKRAS VAF); and (C) CTCs (CTCs/mL of blood) in locally advanced and metastatic cohorts. (A) P values displayed represent the results of a two-tailed, two-sample t-test and (B) and (C) Wilcoxon rank-sum tests as variables were non-normally distributed. Kaplan-Meier survival curves stratified by (D) cfDNA concentration ≥ 15 ng/mL or < 15 ng/mL; (E) ctKRAS VAF ≥ 0.05 or < 0.05; and (F) CTCs ≥ 1/mL or < 1/mL. Binary cutoffs were chosen as discussed in the Statistical Methods section. P values represent the result of a log-rank test comparing the survival curves across reported strata. Numbers of patients at risk at each time point for each group are presented below Kaplan-Meier curves. cfDNA, cell-free DNA; CTC, circulating tumor cell; ctKRAS, circulating tumor KRAS; OS, overall survival; VAF, variant allele fraction.

FIG 2.

Assessment of OS by CTC and ctKRAS status by (A) the Kaplan-Meier method in patients with mPDAC along with the number of patients at risk and (B) by univariate Cox proportional hazards modeling in patients with mPDAC. Patients were categorized as dual negative for CTCs and ctKRAS (CTCs < 1/mL and ctKRAS VAF < 0.05), single positive (CTCs ≥ 1/mL or ctKRAS VAF ≥ 0.05), or dual positive (CTCs ≥ 1/mL and ctKRAS VAF ≥ 0.05). Twenty-one patients with mPDAC were dual negative, 22 were single positive, and 10 were dual positive. Among patients with mPDAC, dual positivity was associated with worse OS than dual negativity (HR, 18.84; 95% CI, 6.38 to 55.68; P < .001) and single positivity was associated with worse OS than dual negativity (HR, 5.98; 95% CI, 2.64 to 13.54; P < .001). CTC, circulating tumor cell; ctKRAS, circulating tumor KRAS; HR, hazard ratio; mPDAC, metastatic pancreatic ductal adenocarcinoma; OS, overall survival; VAF, variant allele fraction.