Prospective study with circulating tumor cells as potential prognosis biomarker in metastatic colorectal cancer.

203 Background: Colorectal cancer (CRC) is one of the most common cancer worldwide. Around 30% present metastatic disease at diagnosis and 50%–60% of patients develop metastasis. New prognostic markers are needed and circulating tumor cells (CTCs) are a promising tool. Methods: Prospective study conducted by blood collection from 75 patients (pts) with metastatic CRC (mCRC), twice, with 2 months interval, together with image exams for therapeutic response evaluation. CTCs were detected by ISET and identified by immunocytochemistry. Results: The mean age was 57.3 years old (24-81). RAS mutations in primary tumor was found in 38% (19/50) of patients (pts) and left colon topography in 41.3% (31/75). Comparing the baseline CTC level (CTC1) with the level at first follow-up (CTC 2), pts with CTC2 – CTC1 > 5.5 per ml demonstrated poor progression-free survival (PFS) (3.2 months) when compared to CTC 2 – CTC1 ≤ 5.5 (9.1 months) (p= 0.005). The median overall survival (OS) was 24.5 months for pts with CTC 1 > 1.5 per ml and 34.2 months for those with CTC1 ≤ 1.5 per (HR=1.89, 95% CI, 1.01 to 3.52; p= 0.041). Patients with RAS mutation (P= 0.001), primary tumor in the right colon (p= 0.014) and expression of Multidrug Resistance Protein 1 in CTCs (p= 0.044) had worse OS. By multivariable analyses, CTC 1 > 1.5/mL (p= 0.025) was an independent prognostic factor. Conclusions: This prospective study confirmed that counts of CTCs at baseline (CTC1) is an important prognostic marker for monitoring mCRC and correlates with other established prognostic factors. Clinical trial information: NCT02979470.