Advanced or multiple polyps likely have a much higher risk of becoming carcinoma.
Adenomatous polyps are neoplastic polyps with a risk of becoming malignant. They are benign glandular tumors that gradually or rapidly grow. Adenomatous polyps have various sizes and may be sessile, flat, or pedunculated. They are likely to precursors of colorectal adenocarcinoma.
credit: large colon video scope Olympus
Adenomatous polyps tend to frequently occur in elderly people. Among healthy people aged 50 years or older, adenomatous polyps occur in more than 15% of women and 25% of men. Adenomatous polyps are likely to be hereditary; for example, people with a positive first-degree family history have a four-fold greater risk of these lesion.
The epithelial cell layer of the large bowel is continuously renewed with a turnover period of 3 to 8 days. Stem cells are differentiated into specialized enterocytes and then migrated toward the lumen. The older epithelial cells are subsequently removed by apoptosis, extrusion, or phagocytes. Adenomatous polyps develop due to an inherited lesion that loses the balance between proliferation and death of epithelial cells. Undifferentiated epithelial cells continuously dive and accumulate on the luminal surface, resulting in adenomatous tissue.
Adenomas are mainly, histologically classified into three types that are tubular adenomas, villous adenomas, and tubulovillous adenomas. Tubular adenomas are the most common type, and constitute 70 to 85% of all adenomas removed by colonoscopies. Tubular adenomas are often small and pedunculated and rarely contain concomitant carcinoma. Villous adenomas are rarer and account for less than 5% of all adenomas. They are generally large and sessile and have a much higher prevalence of carcinoma. Tubulovillous adenomas constitute 10 to 25% of all adenomas and have a mixture of tubular and villous types. Patients with advanced adenomas or multiple adenomas (three or more) are at much greater risk for carcinoma.