A histopathological rarity: Primary signet ring cell carcinoma arising within a colonic villous adenoma

Signet ring cell carcinoma (SRCC) has been described most frequently in the stomach. It may also occur in other mucinous organs like the urinary bladder, prostate, pancreas, breast, lung etc. Within the gastrointestinal tract, up to 99% of SRCC arise in the stomach. SRCC is rare in the colorectal region as compared to the conventional adenocarcinoma, the incidence rates among all colorectal cancers ranging from 0.01% to 2.6%.[1] Even more unusual is the occurrence of a primary SRCC developing within colonic adenomatous polyps. There have been less than eight instances in literature documenting this rare phenomenon.[1-6] This paper reports an additional case of primary SRCC arising in a colonic adenoma.