Epithelial misplacement after biopsy of colorectal adenomas

The question has been raised as to whether the removal of biopsy material from colorectal adenomas can lead to misplacement of tumour fragments into the deeper layers of the bowel wall. We carried out an analysis of histological sections obtained from 21 patients in whom, between 2 and 21 days before removal of their adenoma, forceps biopsy (n = 18), or polypectomy (n = 3) had been performed. The initial histological picture a few days after biopsy is of an ulcer covered by a suppurative exudate and abundant mucus-containing small, free-lying groups of tumour cells. After an average of 7 days, we found misplacement of these groups of cells into the submucosa where, during the course of reparative processes, they became embedded within a capillary-rich granulation tissue. Subsequently, fibrosis of the submucosa develops with persistent mucus pools. Our results thus show that removal of biopsy material from adenomas can result in misplacement of tumour particles into the submucosa. These changes were observed in flat or broad-based tumours, and epithelial misplacement appears to be detectable within only a short period after biopsy. For the differential diagnosis, it is important to distinguish these changes from invasive carcinoma.