A colorectal polyp is a polyp (fleshy growth) occurring on the lining of the colon or rectum. Untreated colorectal polyps can develop into colorectal cancer.Colorectal polyps are often classified by their behaviour (i.e. benign vs. malignant) or cause (e.g. as a consequence of inflammatory bowel disease). They may be benign (e.g. hyperplastic polyp), pre-malignant (e.g. tubular adenoma) or malignant (e.g. colorectal adenocarcinoma). Signs and symptoms
Colorectal polyps are not usually associated with symptoms. When they occur, symptoms include bloody stools; changes in frequency or consistency of stools (such as a week or more of constipation or diarrhoea); and fatigue arising from blood loss. Anemia arising from iron deficiency can also present due to chronic blood loss, even in the absence of bloody stools. Another symptom may be an increased mucus production especially those involving villous adenomas. Copious production of mucous causes loss of potassium that can occasionally result in symptomatic hypokalemia. Occasionally, if a polyp is big enough to cause a bowel obstruction, there may be nausea, vomiting and severe constipation. Structure
Polyps are either pedunculated (attached to the intestinal wall by a stalk) or sessile (grow directly from the wall). : 1342   In addition to the gross appearance categorization, they are further divided by their histologic appearance as tubular adenoma which are tubular glands, villous adenoma which are long finger like projections on the surface, and tubulovillous adenoma which has features of both.
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Genetics
Hereditary syndromes causing increased colorectal polyp formation include:

Familial adenomatous polyposis (FAP)
Hereditary nonpolyposis colorectal cancer
Peutz–Jeghers syndrome
Juvenile polyposis syndromeSeveral genes have been associated with polyposis, such as GREM1, MSH3, MLH3, NTHL1, RNF43 and RPS20. Familial adenomatous polyposis
Familial adenomatous polyposis (FAP) is a form of hereditary cancer syndrome involving the APC gene located on chromosome q521. The syndrome was first described in 1863 by Virchow on a 15-year-old boy with multiple polyps in his colon. The syndrome involves development of multiple polyps at an early age and those left untreated will all eventually develop cancer. The gene is expressed 100% in those with the mutation and it is autosomal dominant. 10% to 20% of patients have negative family history and acquire the syndrome from spontaneous germline mutation. The average age of newly diagnosed patient is 29 and the average age of newly discovered colorectal cancer is 39. It is recommended that those affected undergo colorectal cancer screening at younger age with treatment and prevention are surgical with removal of affected tissues. Hereditary nonpolyposis colorectal cancer (Lynch Syndrome)
Hereditary nonpolyposis colorectal cancer (HNPCC, also known as Lynch syndrome) is a hereditary colorectal cancer syndrome. It is the most common hereditary form of colorectal cancer in the United States and accounts for about 3% of all cases of cancer. It was first recognized by Alder S. Warthin in 1885 at the University of Michigan.