Hamartomatous polyp syndromes
• Hamartomatous polyps include juvenile hamartomatous polyp and the hamartomatous polyp of Peutz-Jeghers type.
• Peutz-Jeghers syndrome involves the entire GI tract (small intestine most common); there is a 93% lifetime risk of cancer. Sporadic Peutz-Jeghers polyps can occur but are extremely rare. Follow-up of these patients is warranted. Histologically, these typically show arborizing smooth muscle bundles in the lamina propria lined by normal or hyperplastic epithelium, occasionally with dysplastic foci.
• Juvenile polyposis syndrome involves the colon or entire GI tract (pedunculated polyps); the risk of CRC is approximately 30% to 40% and is less (10% to 15%) for upper GI cancer. This is the most common polyp in the juvenile population. Germline mutation in SMAD4/DPC4 tumor suppressor gene accounts for half the cases. Histologically, these are lobulated polyps with cystically dilated crypt (mucus retention cysts) with inflamed edematous lamina propria and occasionally with superficial erosions. Other than juvenile polyp syndromes, juvenile polyps are seen in Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome.
• Cowden syndrome involves the entire GI tract from esophagus to rectum; the risk of developing CRC is generally not increased. The most commonly recognized cancer is breast, followed by thyroid. It arises from PTEN germline mutation. Histologically, juvenile polyps are common; also seen are HPs, adenomas, lipomas, and, rarely, ganglioneuromas.
• Bannayan-Riley-Ruvalcaba syndrome is a variant of Cowden syndrome with similar histologic features.
• Cronkhite-Canada syndrome occurs in any portion of the GI tract (sessile polyps); the risk of developing cancer is not well described. Histologically, the polyps seen are similar to juvenile-type (retention) polyps with marked edema in the lamina propria; the intervening mucosa shows similar changes in the lamina propria. Differential diagnosis includes Ménétrier disease and juvenile polyposis syndrome.
• Hyperplastic polyposis is a rare syndrome with an increased risk for CRC. It is characterized by the presence of HPs predominantly (adenomas—tubular or serrated also can be seen) in the colon proximal to sigmoid colon. The number of polyps ranges from 5 to 100. Most of these are nonfamilial and the genetic abnormalities include BRAF and KRAS mutations. All are hereditary except Cronkhite-Canada syndrome and hyperplastic polyposis.