e14056 Background: An efficient anti-tumor immune-response is considered a critical factor for a good outcome and a prolonged survival in colorectal cancer patients. The extent of tumor infiltration by different T-lymphocyte subsets, which represents patients’ state of immune-competence, may reflect a completely different outcome. We have evaluated in advanced colorectal cancer patients the prognostic role of tumor infiltration by cytotoxic (CD8+) T cells expressing the chemokine receptor 7 (CCR7). We also investigated if the presence of this lymphocyte subset might correlate with tumor infiltration by regulatory (Treg) T cells. Methods: The infiltration of CD3+, CD8+, CD4+, CD8+CCR-7+ (Tccr7) and CD4+FoxP3+- (Treg) -T lymphocytes was investigated by immunohistochemistry in the tumor samples at diagnosis of 76 advanced colorectal cancer patients. We searched for a possible correlation of Tccr7 tumor infiltration score with either Treg tumor infiltration extent and patient outcome. Results: High Tccr7 tumor infiltration score was highly predictive of a prolonged overall survival (OS) [high v.s. low score: 41.3 months (95%CI: 30.7-51.9) v.s. 26 (95% CI: 20.6-33.2) months, hazard ratio (HR) = 0.52 (95 %CI: 0.27-0.99); P=0.048)] with a trend to a better treatment related survival and time to progression to first-line chemotherapy. No correlation by regression curve analysis could be demonstrated between Tccr7 and Treg tumor infiltration scores; however, a cluster of patients with a concomitant high infiltration by both T cell populations was identified, who presented a very positive outcome [double high v.s. double low tumor infiltration score: OS= 44 months (95%CI: 27.5-60.4) v.s. 26.1 (95%CI:18.3-34); HR= 0.41 (95%CI: 0.20- 0.93); P=0.03). Conclusions: High Tccr7 tumor infiltration at diagnosis represents a favorable prognostic factor for advanced colorectal cancer patients. A critical role of local immune-response for the long term survival of colorectal cancer patients is suggested.