Malignancies in a Polyp
Invades head of polyp
In situ in a polyp
(1) Invades submucosa
Invades stalk of polyp
In lamina propria
Graphic from CS Steering Committee Training Materials
The adenomatous polyp or polypoid adenoma is the precursor to adenocarcinoma of the colon. 85% of adenocarcinomas of the colon evolve from adenomatous polyps. The majority of adenomatous polyps are benign, but they may transpose to malignancy. Those malignancies may be in situ (non-invasive) or invasive. The diagram shows examples of polypoid malignancies.
Going clockwise starting in the lower left corner, the first malignancy in the polyp invades the submucosa. The second malignancy is non-invasive (in situ) in a polyp. The third malignancy is invasive and invades the head of the polyp. The fourth malignancy is also invasive and invades the stalk of the polyp. The fifth lesion does not go beyond the lamina propria of the mucosa. The sixth malignancy invades the muscularis mucosa but does not go into the submucosa.