Circulating Tumor Cells Predict Occult Metastatic Disease and Prognosis in Pancreatic Cancer

Abstract

Background: Occult metastatic tumors, below imaging thresholds, are a limitation of staging systems that rely on cross-sectional imaging alone and are a cause of the routine understaging of pancreatic ductal adenocarcinomas (PDACs). We investigated circulating tumor cells (CTCs) as a preoperative predictor of occult metastatic disease and as a prognostic biomarker for PDAC patients.

Experimental design: A total of 126 patients (100 with cancer, 26 with benign disease) were enrolled in our study and CTCs were identified and enumerated from 4 mL of venous blood using the microfluidic NanoVelcro assay. CTC enumeration was correlated with clinicopathologic variables and outcomes following both surgical and systemic therapies.

Results: CTCs were identified in 78% of PDAC patients and CTC counts correlated with increasing stage (ρ = 0.42, p < 0.001). Of the 53 patients taken for potentially curative surgery, 13 (24.5%) had occult metastatic disease intraoperatively. Patients with occult disease had significantly more CTCs than patients with local disease only (median 7 vs. 1 CTC, p < 0.0001). At a cut-off of three or more CTCs/4 mL, CTCs correctly identified patients with occult metastatic disease preoperatively (area under the receiver operating characteristic curve 0.82, 95% confidence interval (CI) 0.76-0.98, p < 0.0001). CTCs were a univariate predictor of recurrence-free survival following surgery [hazard ratio (HR) 2.36, 95% CI 1.17-4.78, p = 0.017], as well as an independent predictor of overall survival on multivariate analysis (HR 1.38, 95% CI 1.01-1.88, p = 0.040).

Conclusions: CTCs show promise as a prognostic biomarker for PDAC patients at all stages of disease being treated both medically and surgically. Furthermore, CTCs demonstrate potential as a preoperative biomarker for identifying patients at high risk of occult metastatic disease.

FIG. 1

Patient enrollment process, radiographic staging, initial treatment decisions, and outcomes for all patients. *Of the 22 patients who died, 20 had experienced a recurrence prior to death. PDAC pancreatic ductal adenocarcinoma

FIG. 2

a CTC count by pretreatment radiographic AJCC stage of disease. Non-malignant refers to the 26 patients with non-malignant pancreatic diseases outlined in Table 1. b Performance of CTCs as a preoperative predictor of occult metastatic disease in the subset of patients with untreated tumors (n = 36). CTC enumeration is displayed for patients with successfully resected tumors versus those found to have occult metastatic disease intraoperatively. c Comparison of the performance of CTCs and CA19-9 in the preoperative detection of patients with occult metastatic disease in the subset of patients with untreated tumors (n = 36). CTC circulating tumor cell, AJCC American Joint Committee on Cancer, VB venous blood, CA19-9 cancer antigen 19-9, AUROC area under the receiver operating characteristic curve

FIG. 3

a Overall survival for all patients diagnosed with PDAC in the study, separated into subsets of patients with resected tumors (n = 40, blue), locally advanced disease treated palliatively (n = 12, yellow), occult metastatic disease (n = 12, orange), or metastatic disease (n = 25, green). Patients with occult metastatic disease had survival similar to patients with radiologically visible metastatic disease, and significantly different from patients with early-stage or locally advanced disease. b Overall survival for all patients stratified by CTC count (n = 100). c Time to recurrence for patients after surgical resection stratified by CTC count (n = 40). CTC circulating tumor cell, PDAC pancreatic ductal adenocarcinoma