Large Tubulo-Villous Adenoma (4 from 6)

Endoscopic View of Enormous Polyp of the Colon

Colon cancer mostly arises from adenomas, recognized as
colonic polyps, but may occasionally arise from the sessile serrated adenoma. Adenomatous polyposis coli (APC) gene mutation is the key molecular step in adenoma formation.
Mismatch repair gene mutation is a less common alternative pathway. Progression from adenomas to colon cancer is a multistep process, involving mutations of the DCC, k-ras, and p53 genes; loss of heterozygosity in which cells loose one allele of some genes from chromosomal loss; and DNA methylation which can silence DNA expression.