Assessment of colorectal cancer molecular features along bowel subsites challenges the conception of distinct dichotomy of proximal versus distal colorectum

Colorectal cancer is typically classified into proximal colon, distal colon and rectal cancer. Tumour genetic and epigenetic features differ by tumour location. Considering a possible role of bowel contents (including microbiome) in carcinogenesis, this study hypothesised that tumour molecular features might gradually change along bowel subsites, rather than change abruptly at splenic flexure.

Utilising 1443 colorectal cancers in two US nationwide prospective cohort studies, the frequencies of molecular features (CpG island methylator phenotype (CIMP), microsatellite instability (MSI), LINE-1 methylation and BRAF, KRAS and PIK3CA mutations) were examined along bowel subsites (rectum, rectosigmoid junction, sigmoid, descending colon, splenic flexure, transverse colon, hepatic flexure, ascending colon and caecum). The linearity and non-linearity of molecular relations along subsites were statistically tested by multivariate logistic or linear regression analysis.