Redefining GALT-associated carcinoma: a distinct subtype of colorectal adenocarcinoma.

We report a case of GALT-associated carcinoma, a rare morphological variant of colorectal adenocarcinoma characterised by cystic glands containing eosinophilic material, set within dense lymphoid stroma with germinal centres. Since its first description in 1999, only 26 cases have been documented. Its association with lymphoid tissue, the presence of intraepithelial lymphocytes, and the absence of goblet cells led to the hypothesis that it may originate from M-cells located in the dome epithelium of gut-associated lymphoid tissue, hence the alternative term "dome-type carcinoma". Through detailed histological, immunohistochemical, ultrastructural and molecular analyses of our case, supported by a comprehensive literature review, we found no evidence supporting M-cell differentiation: intraepithelial B lymphocytes were absent, GP2 immunostaining was negative and ultrastructural features were inconsistent with M-cell morphology. Nevertheless, the lesion's pushing growth pattern, lack of high-risk histopathological features and indolent behaviour justify its recognition as a distinct morphological subtype of colorectal cancer.