Squamous metaplasia within a sigmoid adenoma. A rare feature.

Squamous metaplasia occurring within a colorectal polyp is a rare finding, having a reported incidence of approximately 0.44%. The origin of the squamous cells in this type of setting is uncertain (mechanical irritation and chronic inflammation are potential predisposing factors). It has been implied that the significance of squamous metaplasia in colorectal adenomas is that of a preneoplastic lesion for squamous cell and adenosquamous carcinoma, however the evidence to support this statement is scarce. We present a case of a large tubulovillous adenoma located in the sigmoid, with low-grade dysplasia and multiple foci of p16-positive immunoexpression squamous metaplasia in a 54-year-old Caucasian male, presenting with rectal bleeding.