Sessile polyps are more likely to avoid detection during screening than pedunculated polyps, which have stalks, as stated by Merck. As a result, sessile polyps are more likely to become cancerous before detection. However, the shape does not influence a polyp's probability of turning into cancer.
All polyps are viewed as pre-cancerous, but without treatment, they can turn into cancer, as stated by About.com. Adenomatous polyps are the most common type, making up about 70 percent of all polyps. It takes years, in most cases, for these polyps to develop into colon cancer. Hyperplastic polyps have an abnormal level of cell growth, but they do not have an elevated risk of turning into cancer. Whether polyps have a stalk or are sessile, doctors remove them to test for cancerous tissue and to keep them from developing into cancerous tissue over time.