Mucinous differentiation in colonic adenocarcinoma is associated with a reduction in tumour-infiltrating lymphocytes

Aims: The aim of this study was to examine the density of tumour-infiltrating lymphocytes (TILs) in colorectal carcinomas showing mucinous differentiation. Methods: We examined 33 adenocarcinomas showing variable mucinous differentiation and compared the density of TILs with that of 65 adenocarcinomas of no special type (NOS) showing no mucinous differentiation. Results: Mucinous differentiation is associated with a significantly lower density of TILs compared to adenocarcinoma NOS (P=0.0016; chi-squared test with continuity correction). This reduction in TILs is present also in adjacent foci of adenocarcinoma NOS within mucinous tumours. Conclusions: There is a reduction in the number of TILs in all areas of colorectal adenocarcinomas that show mucinous differentiation, which may help explain the increased biological aggressiveness associated with this pattern of differentiation.