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 ₀ , D ₁₄ , D ₂₈ , D ₄₂ , and D ₅₆ (EPISPOT assay) and at D ₀ and D ₂₈ (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 ₀ ), 15% (D ₁₄ ), 12% (D ₂₈ ), 10% (D ₄₂ ), and 12% (D ₅₆ ) of 155 patients. PFS and OS were shorter in patients who remained positive, with viable CTCs between D ₀ and D ₂₈ compared with the other patients (PFS = 7.36 vs. 9.43 months, p = 0.0161 and OS = 25.99 vs. 13.83 months, p = 0.0178). The prognostic and predictive values of ≥3 CTCs (CellSearch ^® system) were confirmed.
Conclusions: CTC detection at D ₂₈ and the D ₀ -D ₂₈ CTC dynamics evaluated with the EPISPOT assay were associated with outcomes and may predict response to treatment.