Value of the combination of intraepithelial tumor-infiltrating lymphocyte density and the heterogeneity of density as a prognostic marker in stage III colorectal cancers.

Tumor-infiltrating lymphocyte (TIL) density is both a prognostic and a predictive factor in colorectal cancer (CRC). Whether the heterogeneity of TIL density across the tumor plays an important role in the clinical outcome of CRC is not well known. Adjuvant chemotherapy-treated patients with stage III CRC were analyzed for survival according to TIL density and density heterogeneity, which were determined on CD8-immunostained slides using a machine learning method and by calculating the Simpson evenness index, respectively. High heterogeneity of the intraepithelial TIL density was found to be an independent prognostic factor, with a hazard ratio of 1.970 (1.207-3.215) in the multivariate analysis of recurrence-free survival. High heterogeneity was closely associated with a high T category, venous invasion, perineural invasion, and <i>KRAS</i> mutation. The combination of both intraepithelial TIL density and density heterogeneity was significantly associated with the prognosis of patients: low TIL density/high TIL heterogeneity showed hazard ratios of 3.284 (1.639-6.578) and 4.176 (1.713-10.178) in the discovery and validation cohorts, respectively. Our findings suggest that the heterogeneity status of intraepithelial TIL density might help delineate patients with better vs. worse survival when combined with intraepithelial TIL density.