Circulating Tumor Cells As Prognostic Markers in Neuroendocrine Tumors

Abstract

Purpose To determine the prognostic significance of circulating tumor cells (CTCs) in patients with neuroendocrine cancer. Patients and Methods In this single-center prospective study, 176 patients with measurable metastatic neuroendocrine tumors (NETs) were recruited. CTCs were measured using a semiautomated technique based on immunomagnetic separation of epithelial cell adhesion molecule–expressing cells. Results Overall, 49% patients had ≥ one CTC, 42% had ≥ two CTCs, and 30% had ≥ five CTCs in 7.5 mL blood. Presence of CTCs was associated with increased burden, increased tumor grade, and elevated serum chromogranin A (CgA). Using a 90-patient training set and 85-patient validation set, we defined a cutoff of < one or ≥ one as the optimal prognostic threshold with respect to progression-free survival (PFS). Applying this threshold, the presence of ≥ one CTC was associated with worse PFS and overall survival (OS; hazard ratios [HRs], 6.6 and 8.0, respectively; both P < .001). In multivariate analysis, CTCs remained significant when other prognostic markers, grade, tumor burden, and CgA were included. Within grades, presence of CTCs was able to define a poor prognostic subgroup. For grade 1, HRs were 5.0 for PFS (P = .017) and 7.2 for OS (P = .023); for grade 2, HRs were 3.5 for PFS (P = .018) and 5.2 for OS (P = .036). Conclusion CTCs are a promising prognostic marker for patients with NETs and should be assessed in the context of clinical trials with defined tumor subtypes and therapy.