Background: Colorectal cancer (CRC), the third most common cancer globally, caused 881,000 cancer deaths in 2018. Toll-like receptors (TLRs), the primary sensors of pathogen-associated molecular patterns and damage-associated molecular patterns, activate innate and adaptive immune systems and participate in the development of an inflammatory tumor microenvironment. We aimed to explore the prognostic value of TLR3, TLR5, TLR7, and TLR9 tissue expressions in CRC patients.

Methods: Using immunohistochemistry, we analyzed tissue microarray samples from 825 CRC patients who underwent surgery between 1982 and 2002 at the Department of Surgery, Helsinki University Hospital, Finland. After analyzing a pilot series of 205 tissue samples, we included only TLR5 and TLR7 in the remainder of the patient series. We evaluated the associations between TLR5 and TLR7 tissue expressions, clinicopathologic variables, and survival. Using the Kaplan-Meier method, we generated survival curves, determining significance using the log-rank test. Univariate and multivariate survival analyses relied on the Cox proportional hazards model.

Results: The 5-year disease-specific survival was 55.9% among TLR5-negative (95% confidence interval [CI] 50.6-61.2%) and 61.9% (95% CI 56.6-67.2%; p = 0.011, log-rank test) among TLR5-positive patients. In the Cox multivariate survival analysis adjusted for age, sex, stage, location, and grade, positive TLR5 immunoexpression (hazard ratio [HR] 0.74; 95% CI 0.59-0.92; p = 0.007) served as an independent positive prognostic factor. TLR7 immunoexpression exhibited no prognostic value in the survival analysis across the entire cohort (HR 0.97; 95% CI 0.78-1.20; p = 0.754) nor in subgroup analyses.

Conclusions: We show for the first time that a high TLR5 tumor tissue expression associates with a better prognosis in CRC patients.