Characteristics and significance of colorectal cancer associated lymphoid reaction

A subset of colorectal cancers (CRCs) exhibits so‐called Crohn's like lymphoid reaction (CLR), an inflammatory reaction pattern that consists of numerous transmural lymphoid aggregates. However, the composition of these aggregates, their biological mechanisms and their prognostic significance are not well‐defined. We analyzed two CRC cohorts (418 and 149 patients) and determined clinicopathological features including survival. A new method for evaluating CLR based on counting the areal density of the lymphoid follicles (CLR density) was adopted. Immune cell densities at intratumoral and peritumoral regions, as well as the composition of the lymphoid follicles, were studied by immunohistochemistry. We found that CLR comprised of lymphoid aggregates with no evidence of granuloma formation. High CLR density associated with lower tumor stage, lack of preoperative radiotherapy or chemoradiotherapy and deficient mismatch repair enzyme expression. CLR density had positive correlations with peritumoral and intratumoral densities of CD83+ mature dendritic cells and T cells. High CLR density associated with better survival and had prognostic value that was independent of stage, Klintrup‐Mäkinen score for peritumoral inflammation and the numbers of tumor infiltrating T cells. CLR density evaluation had excellent intraobserver and interobserver agreement. In conclusion, the results suggest that CLR contributes to the adaptive antitumor immunity. Quantitative evaluation of CLR density is a relevant prognostic indicator in CRC. What's new? Some colorectal cancers exhibit an inflammatory response called the Crohn's‐like lymphoid reaction (CLR), in which lymphoid aggregates form around tumors. It's not clear yet, however, what these aggregates reveal about cancer prognosis. In this study, the authors report a new method for quantifying the density of the CLR; they then compared the CLR with the prevalence of different immune cell types in the tumor area. The number of mature DC cells correlated closely with the density of the lymphoid aggregates, suggesting that the CLR plays a role in adaptive tumor immunity. High CLR density correlated with low tumor stage, but also correlated with better survival regardless of stage.