Low number of detectable circulating tumor cells in non-metastatic colon cancer.

Background: The aim of the present study was to detect circulating tumor cells (CTCs) in the peripheral blood of patients with non-metastatic colon cancer and to evaluate whether there is a diurnal variation in the CTC counts. Furthermore, the study aimed to examine the correlation between CTCs and TNM stage, other paraclinical variables and prognosis. Patients and Methods: Blood samples were collected from 20 consecutive patients with colon cancer TNM stage I-III at four different perioperative time points. Detection of CTCs was performed using the immunological assay CellSearch ® . Results: CTCs were detected in 1 out of 60 preoperative blood samples, resulting in a detection rate of 1 in 20 patients (5%; 95% confidence interval=0.1-25%). None of the postoperative blood samples had CTC levels above the cut-off value (≥2 CTCs/7.5ml blood). Conclusion: The presence of CTCs in non-metastatic colon cancer is rare and barely detectable with the only commercially available assay for detection of CTCs, the CellSearch System. The presence of circulating tumor cells (CTCs) in the peripheral blood of patients with metastatic breast, prostate and colorectal cancer has proven to be a strong prognostic marker (1-4). Two prospective studies have evaluated CTCs in patients with metastatic colorectal cancer and demonstrated that the presence of CTCs was an independent predictor of decreased progression-free survival and overall survival (1, 4). These studies used the only commercially available assay for detection of CTC, VERIDEX, the CellSearch ® , Circulating Tumor Cell Test (LLC). This semiautomated immunological technique has been approved by the US Food and Drug Administration for the detection of CTCs in metastatic breast, prostate and colorectal cancer. Allard et al. (5) evaluated the CellSearch System and established a cut-off value of ≥2 CTCs per 7.5 ml peripheral blood in patients with various metastatic carcinomas. With this method, CTCs were detectable in approximately 30% of patients with metastatic colorectal cancer (1, 4). Only a few studies have utilized the CellSearch System in non-metastatic colorectal cancer. Sastre et al. (6) demonstrated that CTCs were detected in 26% of patients tested postoperatively, but two other studies reported lower detection rates, 7% of patients tested preoperatively (7) and 15% of patients tested postoperatively with the Cellsearch assay (8). There are no data on the prognostic significance of CTCs in non-metastatic colorectal cancer applying the CellSearch assay. With reference to these results a study was conducted to determine the presence of CTCs pre- and postoperatively in patients with non-metastatic colon cancer. The aims were: to evaluate whether there was a diurnal variation of CTCs preoperatively, to correlate the presence of CTCs with TNM- stage and other paraclinical variables and to determine whether the postoperative presence of CTCs predicts recurrence.