Most juvenile polyps are benign, however, malignancy can occur. The cumulative lifetime risk of colorectal cancer is 39% in patients with juvenile polyposis syndrome.

Diet and lifestyle are believed to play a large role in whether colorectal polyps form. Studies show there to be a protective link between consumption of cooked green vegetables, brown rice, legumes, and dried fruit and decreased incidence of colorectal polyps.

The incidence of the mutation is between 1 in 10,000 and 1 in 15,000 births.

By age 35 years, 95% of individuals with FAP (>100 adenomas) have polyps. Without colectomy, colon cancer is virtually inevitable. The mean age of colon cancer in untreated individuals is 39 years (range 34–43 years).

Attentuated FAP arises when APC is defective but still somewhat functional. As a result, it retains part of its ability to suppress polyps. Therefore, attenuated FAP manifests as colorectal cancer unusually late (age 40–70, average=55), and typically with few, or at least far fewer polyps (typically 30), than the more usual version of FAP, at an age when FAP is no longer considered much of a likelihood or risk according to usual FAP epidemiology.

Most patients will develop flat, brownish spots (melanotic macules) on the skin, especially on the lips and oral mucosa, during the first year of life, and a patient’s first bowel obstruction due to intussusception usually occurs between the ages of six and 18 years. The cumulative lifetime cancer risk begins to rise in middle age. Cumulative risks by age 70 for all cancers, gastrointestinal (GI) cancers, and pancreatic cancer are 85%, 57%, and 11%, respectively.

A 2011 Dutch study followed 133 patients for 14 years. The cumulative risk for cancer was 40% and 76% at ages 40 and 70, respectively. 42 (32%) of the patients died during the study, of which 28 (67%) were cancer related. They died at a median age of 45. Mortality was increased compared with the general population.

A family with sinonasal polyposis were followed up for 28 years. Two cases of sinonasal type adenocarcinoma developed. This is a rare cancer. This report suggested that follow up of sinus polyps in this syndrome may be indicated.

Fundic gland polyps are found in 0.8 to 1.9% of patients who undergo esophagogastroduodenoscopy, and are more common in middle aged women.

The most important consideration in evaluating patients with FGPs is distinguishing between sporadic form (patients without any other gastrointestinal condition, usually in middle age with female prevalence) and syndromic form. This is to ascertain the risk of development of gastric cancer, and to ascertain the risk of concomitant colon cancer.

FGPs can be found in association with the following genetic conditions:

- familial adenomatous polyposis

- attenuated familial adenomatous polyposis syndromes

- Zollinger-Ellison syndrome

- gastric adenocarcinoma associated with proxymal polyposis of the stomach (GAPPS): this condition, described in three families is characterized by development of antral adenomas and FGPs, with early development of severe dysplasia and gastric cancer, in absence of overt intestinal polyposis. This condition has been recently characterized by a point mutation in exon 1B of APC gene.

Sporadic FGPs have been associated with:

- chronic use of proton pump inhibitors (proposed by some authors, denied by others)

- "Helicobacter pylori" infection: there is a reverse relationship between infection and fundic gland polyps, and infection by "H pylori" causes polyps regression.

Complete removal of a SSA is considered curative.

Several SSAs confer a higher risk of subsequently finding colorectal cancer and warrant more frequent surveillance. The surveillance guidelines are the same as for other colonic adenomas. The surveillance interval is dependent on (1) the number of adenomas, (2) the size of the adenomas, and (3) the presence of high-grade microscopic features.

Colorectal polyps can be detected using a faecal occult blood test, flexible sigmoidoscopy, colonoscopy, virtual colonoscopy, digital rectal examination, barium enema or a pill camera.

Malignant potential is associated with

- degree of dysplasia

- Type of polyp (e.g. villous adenoma):

- Tubular Adenoma: 5% risk of cancer

- Tubulovillous adenoma: 20% risk of cancer

- Villous adenoma: 40% risk of cancer

- Size of polyp:

- <1 cm =<1% risk of cancer

- 1 cm=10% risk of cancer

- 2 cm=15% risk of cancer

Normally an adenoma which is greater than 0.5 cm is treated

Screening for colonic polyps as well as preventing them has become an important part of the management of the condition. Medical societies have established guidelines for colorectal screening in order to prevent adenomatous polyps and to minimize the chances of developing colon cancer. It is believed that some changes in the diet might be helpful in preventing polyps from occurring but there is no other way to prevent the polyps from developing into cancerous growths than by detecting and removing them.

According to the guidelines established by the American Cancer Society, individuals who reach the age of 50 should perform an occult blood test yearly. Colon polyps as they grow can sometimes cause bleeding within the intestine, which can be detected with the help of this test. Also, persons in their 50s are recommended to have flexible sigmoidoscopies performed once in 3 to 5 years to detect any abnormal growth which could be an adenomatous polyp. If adenomatous polyps are detected during this procedure, it is most likely that the patient will have to undergo a colonoscopy. Medical societies recommend colonoscopies every ten years starting at age 50 as a necessary screening practice for colon cancer. The screening provides an accurate image of the intestine and also allows the removal of the polyp, if found. Once an adenomatous polyp is identified during colonoscopy, there are several methods of removal including using a snare or a heating device. Colonoscopies are preferred over sigmoidoscopies because they allow the examination of the entire colon; a very important aspect, considering that more than half of the colonic polyps occur in the upper colon, which is not reached during sigmoidoscopies.

It has been statistically demonstrated that screening programs are effective in reducing the number of deaths caused by colon cancer due to adenomatous polyps. While there are risks of complications associated with colonoscopies, those risks are extremely low at approximately 0.35 percent. For comparison, the lifetime risk of developing colon cancer is around 6 percent. As there is a small likelihood of recurrence, surveillance after polyp removal is recommended.

An adenoma (from Greek αδένας, "", "gland" + -ώμα, "", "tumor") (; plural adenomas or adenomata ) is a benign tumor of epithelial tissue with glandular origin, glandular characteristics, or both. Adenomas can grow from many glandular organs, including the adrenal glands, pituitary gland, thyroid, prostate, and others. Some adenomas grow from epithelial tissue in nonglandular areas but express glandular tissue structure (as can happen in familial polyposis coli). Although adenomas are benign, over time they may transform to become malignant, at which point they are called adenocarcinomas. Most adenomas do not transform. But even while benign, they have the potential to cause serious health complications by compressing other structures (mass effect) and by producing large amounts of hormones in an unregulated, non-feedback-dependent manner (causing paraneoplastic syndromes). Some adenomas are too small to be seen macroscopically but can still cause clinical symptoms.

Because Cowden syndrome can be difficult to diagnose, the exact prevalence is unknown; however, it probably occurs in at least 1 in 200,000 people.

A 2010 review of 211 patients (21 from one center, and the remaining 190 from the external literature) studied the risks for cancer and Lhermitte-Duclos disease in Cowden syndrome patients.

The cumulative lifetime (age 70 years) risks were 89% for any cancer diagnosis (95% confidence interval (CI) = 80%,95%), breast cancer [female] 81% (CI = 66%,90%), LDD 32% (CI = 19%,49%), thyroid cancer 21% (CI = 14%,29%), endometrial cancer 19% (CI = 10%,32%) and renal cancer 15% (CI = 6%,32%). A previously unreported increased lifetime risk for colorectal cancer was identified (16%, CI = 8%,24%). Male CS patients had fewer cancers diagnosed than female patients and often had cancers not classically associated with CS.

A physician's response to detecting an adenoma in a patient will vary according to the type and location of the adenoma among other factors. Different adenomas will grow at different rates, but typically physicians can anticipate the rates of growth because some types of common adenomas progress similarly in most patients. Two common responses are removing the adenoma with surgery and then monitoring the patient according to established guidelines.

One common example of treatment is the response recommended by specialty professional organizations upon removing adenomatous polyps from a patient. In the common case of removing one or two of these polyps from the colon from a patient with no particular risk factors for cancer, thereafter the best practice is to resume surveillance colonoscopy after 5–10 years rather than repeating it more frequently than the standard recommendation.

In gastroenterology, a sessile serrated adenoma (abbreviated SSA), also known as sessile serrated polyp (abbreviated SSP), is a premalignant flat (or sessile) lesion of the colon, predominantly seen in the cecum and ascending colon.

SSAs are thought to lead to colorectal cancer through the (alternate) "serrated pathway". This differs from most colorectal cancer, which arises from mutations starting with inactivation of the APC gene.

Multiple SSAs may be part of the "serrated polyposis syndrome".

Juvenile Polyposis Syndrome can occur sporadically in families or be inherited in an autosomal dominant manner.

Two genes associated with Juvenile Polyposis Syndrome are BMPR1A and SMAD4. Gene testing may be useful when trying to ascertain which non-symptomatic family members may be at risk of developing polyps, however having a known familial mutation would be unlikely to change the course of treatment. A known mutation may also be of use for affected individuals when they decide to start a family as it allows them reproductive choices.

While mutations in the gene PTEN were also thought to have caused Juvenile Polyposis Syndrome, it is now thought that mutations in this gene cause a similar clinical picture to Juvenile Polyposis Syndrome but are actually affected with Cowden syndrome or other phenotypes of the PTEN hamartoma tumor syndrome.

Benign tumors are very diverse, and may be asymptomatic or may cause specific symptoms depending on their anatomic location and tissue type. They grow outwards, producing large rounded masses, which can cause what is known as a "mass effect". This growth can cause compression of local tissues or organs, which can cause many effects such as blockage of ducts, reduced blood flow (ischaemia), tissue death (necrosis) and nerve pain or damage. Some tumors also produce hormones that can lead to life-threatening situations. Insulinomas can produce large amounts of insulin leading to hypoglycemia. Pituitary adenomas can cause elevated levels of hormones such as growth hormone and insulin-like growth factor-1, which cause acromegaly; prolactin; ACTH and cortisol, which cause Cushings disease; TSH, which causes hyperthyroidism; and FSH and LH. Bowel intussusception can occur with various benign colonic tumors. Cosmetic effects can be caused by tumors, especially those of the skin, possibly causing psychological effects on the person with the tumor. Vascular tumors can bleed, which in some cases can be substantial, leading to anemia.

PTEN hamartoma syndrome comprises four distinct hamartomatous disorders characterised by genetic mutations in the PTEN gene; Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome and Proteus-like syndrome. Although they all have distinct clinical features, the formation of hamartomas is present in all four syndromes. PTEN is a tumor suppressor gene that is involved in cellular signalling. Absent or dysfunctional PTEN protein allows cells to over-proliferate, causing hamartomas.

Cowden syndrome is an autosomal dominant genetic disorder characterised by multiple benign hamartomas (trichilemmomas and mucocutaneous papillomatous papules) as well as a predisposition for cancers of multiple organs including the breast and thyroid. Bannayan-Riley-Ruvalcaba syndrome is a congenital disorder characterised by hamartomatous intestinal polyposis, macrocephaly, lipomatosis, hemangiomatosis and glans penis macules. Proteus syndrome is characterised by nevi, asymmetric overgrowth of various body parts, adipose tissue dysregulation, cystadenomas, adenomas, vascular malformation.

There is a risk of development of cancer with fundic gland polyposis, but it varies based on the underlying cause of the polyposis. The risk is highest with congenital polyposis syndromes, and is lowest in acquired causes. As a result, it is recommended that patients with multiple fundic polyps have a colonoscopy to evaluate the colon. If there are polyps seen on colonoscopy, genetic testing and testing of family members is recommended.

In the gastric adenocarcinoma associated with proximal polyposis of the stomach (GAPPS), there is a high risk of early development of proximal gastric adenocarcinoma.

It is still unclear which patients would benefit with surveillance gastroscopy, but most physicians recommend endoscopy every one to three years to survey polyps for dysplasia or cancer. In the event of high grade dysplasia, polypectomy, which is done through the endoscopy, or partial gastrectomy may be recommended. One study showed the benefit of NSAID therapy in regression of gastric polyps, but the efficacy of this strategy (given the side effects of NSAIDs) is still dubious.

The risks of progression to colorectal cancer increases if the polyp is larger than 1 cm and contains a higher percentage of villous component. Also, the shape of the polyps is related to the risk of progression into carcinoma. Polyps that are pedunculated (with a stalk) are usually less dangerous than sessile polyps (flat polyps). Sessile polyps have a shorter pathway for migration of invasive cells from the tumor into submucosal and more distant structures, and they are also more difficult to remove and to ascertain. Sessile polyps larger than 2 cm usually contain villous features, have a higher malignant potential, and tend to recur following colonoscopic polypectomy.

Although polyps do not carry significant risk of colon cancer, tubular adenomatous polyps may become cancerous when they grow larger. Larger tubular adenomatous polyps have an increased risk of malignancy when larger because then they develop more villous components and may become sessile.

It is estimated that an individual whose parents have been diagnosed with an adenomatous polyp has a 50% greater chance to develop colon cancer than individuals with no family history of colonic polyps. At this point, there is no method to establish the risks that patients with a family history of colon polyps have to develop these growths. Overall, nearly 6% of the population, regardless of the family history, is at risk of developing colon cancer.

Polypoid lesions of the gallbladder affect approximately 5% of the adult population. The causes are uncertain, but there is a definite correlation with increasing age and the presence of gallstones (cholelithiasis). Most affected individuals do not have symptoms. The gallbladder polyps are detected during abdominal ultrasonography performed for other reasons.

The incidence of gallbladder polyps is higher among men than women. The overall prevalence among men of Chinese ancestry is 9.5%, higher than other ethnic types.

Muir–Torre was observed to occur in 14 of 50 families (28%) and in 14 of 152 individuals (9.2%) with Lynch syndrome, also known as HNPCC.

The 2 major MMR proteins involved are hMLH1 and hMSH2. Approximately 70% of tumors associated with the MTS have microsatellite instability. While germline disruption of hMLH1 and hMSH2 is evenly distributed in HNPCC, disruption of hMSH2 is seen in greater than 90% of MTS patients.

Gastrointestinal and genitourinary cancers are the most common internal malignancies. Colorectal cancer is the most common visceral neoplasm in Muir–Torre syndrome patients.

Attenuated familial adenomatous polyposis is a form of familial adenomatous polyposis, a cancer syndrome. It is a pre-malignant disease that can develop into colorectal cancer. A patient will have fewer than a hundred polyps located typically in right side of the colon. Cancer might develop as early as the age of five, though typically presents later than classical FAP.

Familial adenomatous polyposis (FAP) is an autosomal dominant inherited condition in which numerous adenomatous polyps form mainly in the epithelium of the large intestine. While these polyps start out benign, malignant transformation into colon cancer occurs when they are left untreated. Three variants are known to exist, FAP and attenuated FAP (originally called hereditary flat adenoma syndrome) are caused by APC gene defects on chromosome 5 while autosomal recessive FAP (or MYH-associated polyposis) is caused by defects in the "MUTYH" gene on chromosome 1. Of the three, FAP itself is the most severe and most common; although for all three, the resulting colonic polyps and cancers are confined to the colon wall and removal can greatly reduce the spread of cancer.

The root cause of FAP is understood to be a genetic mutation—a flaw in the body's tumour suppressor genes that prevent development of tumours. The flaw allows numerous cells of the intestinal wall to develop into potentially cancerous polyps when they would usually reach the end of their life; inevitably one or more will eventually progress and give rise to cancer (7% risk by age 21, rising to 87% by age 45 and 93% by age 50). The flawed genes do not trigger cancer, but rather, they reduce the body's ability to protect against the risk of aged cells becoming cancerous. Even with the flawed gene, it may still take time before a cell actually does develop that is cancerous as a result, and the gene may in some cases still partially operate to control tumours, therefore cancer from FAP takes many years to develop and is almost always an adult-onset disease.

The second form of FAP, known as attenuated familial adenomatous polyposis has the APC gene functional but slightly impaired. It is therefore somewhat able to operate as usual. Attenuated FAP still presents a high 70% lifetime risk of cancer (as estimated), but typically presents with far fewer polyps (typically 30) rather than the hundreds or thousands usually found in FAP, and arises at an age when FAP is usually no longer considered likely—typically between 40 and 70 years old (average 55) rather than the more usual 30's upward. Because it has far fewer polyps, options for management may be different.

The third variant, autosomal recessive familial adenomatous polyposis or MYH-associated polyposis, is also milder and, as its name suggests, requires both parents to be 'carriers' to manifest the condition.

In some cases FAP can manifest higher in the colon than usual (for example, the ascending colon, or proximal to the splenic flexure, or in the gastric or duodenal tracts) where they show no symptoms until cancer is present and greatly advanced. APC mutations have been linked to certain other cancers such as thyroid cancer. As the mutation causing FAP is genetic, it can be inherited hereditarily from either parent, and passed to children. A genetic blood test of the APC gene exists that can determine whether it is deficient, and therefore can predict the possibility of FAP. Individuals at risk (due to family links or genetic testing) are usually offered routine monitoring of the intestinal tract every 1 – 5 years for life, from early adulthood, to detect the slow-forming polyps and act if found, before they can pose a threat. International polyposis registries exists that track known cases of FAP or APC gene defects, for research and clinical purposes. Mutation of APC also occurs commonly in incident cases of colorectal carcinoma, emphasizing its importance in this form of cancer.

This is a very rare tumor, since only about 1 in 35,000 to 40,000 people have VHL, of whom about 10% have endolymphatic sac tumors. Patients usually present in the 4th to 5th decades without an gender predilection. The tumor involves the endolymphatic sac, a portion of the intraosseous inner ear of the posterior petrous bone.

Gardner syndrome, also known as Gardner's syndrome or familial colorectal polyposis, is an autosomal dominant form of polyposis characterized by the presence of multiple polyps in the colon together with tumors outside the colon. The extracolonic tumors may include osteomas of the skull, thyroid cancer, epidermoid cysts, fibromas, as well as the occurrence of desmoid tumors in approximately 15% of affected individuals.

Desmoid tumors are fibrous tumors which usually occur in the tissue covering the intestines and may be provoked by surgery to remove the colon. The countless polyps in the colon predispose to the development of colon cancer; if the colon is not removed, the chance of colon cancer is considered to be very significant. Polyps may also grow in the stomach, duodenum, spleen, kidneys, liver, mesentery and small bowel. In a small number of cases, polyps have also appeared in the cerebellum. Cancers related to Gardner syndrome commonly appear in the thyroid, liver and kidneys. The number of polyps increases with age, and hundreds to thousands of polyps can develop in the colon.

The syndrome was first described in 1951. There is no cure at this time, and in its more advanced forms, it is considered a terminal diagnosis with a life expectancy of 35–45 years; treatments are surgery and palliative care, although some chemotherapy has been tried with limited success.

Patients are usually managed by a multidisciplinary team including surgeons, gynecologists, and dermatologists because of the complex nature of this disorder. Follow-up for the increased risk of breast cancer risk includes monthly breast self-examination, annual breast examination, and mammography at age 30 or five years earlier than the youngest age of breast cancer in the family. The magnitude of the risk of breast cancer justifies routine screening with breast MRI as per published guidelines.

Gardner syndrome is inherited in an autosomal dominant manner. Typically, one parent has Gardner syndrome. Each of their children, male and female alike, are at 50% risk of inheriting the gene for Gardner syndrome.