Clinical Relevance of Viable Circulating Tumor Cells in Patients with Metastatic Colorectal Cancer: The COLOSPOT Prospective Study.

Background: Circulating tumor cells (CTCs) allow the real-time monitoring of tumor course and treatment response. This prospective multicenter study evaluates and compares the early predictive value of CTC enumeration with EPISPOT, a functional assay that detects only viable CTCs, and with the CellSearch system in patients with metastatic colorectal cancer (mCRC).

Methods: Treatment-naive patients with mCRC and measurable disease (RECIST criteria 1.1) received FOLFIRI-bevacizumab until progression or unacceptable toxicity. CTCs in peripheral blood were enumerated at D, D, D, D, and D (EPISPOT assay) and at D and D (CellSearch system). Progression-free survival (PFS) and overall survival (OS) were assessed with the Kaplan-Meier method and log-rank test.

Results: With the EPISPOT assay, at least 1 viable CTC was detected in 21% (D), 15% (D), 12% (D), 10% (D), and 12% (D) of 155 patients. PFS and OS were shorter in patients who remained positive, with viable CTCs between D and D compared with the other patients (PFS = 7.36 vs. 9.43 months, = 0.0161 and OS = 25.99 vs. 13.83 months, = 0.0178). The prognostic and predictive values of ≥3 CTCs (CellSearch system) were confirmed.

Conclusions: CTC detection at D and the D-D CTC dynamics evaluated with the EPISPOT assay were associated with outcomes and may predict response to treatment.