The most common general classification is:

- hyperplastic,

- neoplastic (adenomatous & malignant),

- hamartomatous and,

- inflammatory.

Colorectal polyps are not usually associated with symptoms. When they occur, symptoms include rectal bleeding, bloody stools, abdominal pain and fatigue. A change in bowel habits may occur including constipation and diarrhoea. Occasionally, if a polyp is big enough to cause a bowel obstruction, there may be nausea, vomiting and severe constipation.

Most patients with fundic gland polyps (FGPs) do not have any symptoms, and the diagnosis is made on gastroscopy done for other reasons. Retrospective analysis of patients with sporadic FGPs shows that a high percentage do have symptoms, but that this is more likely to be related to the underlying disease responsible for the polyposis. These symptoms include:

- epigastric pain

- nausea

- vomiting

- weight loss

The polyps on endoscopy are usually tiny, numerous and sessile, and usually scattered throughout the fundus of the stomach, where parietal cells are more numerous. They have the same colour as the gastric mucosa, and never have a stalk.

When the polyps are biopsied, the pathology typically shows shortened gastric pits, and both superficial and deep cystic lesions in the fundic glands, lined by all three types of cells of acid-producing mucosa: mucous, parietal and chief cells. As sometimes parietal cell hyperplasia may develop deep dilations of gland, one should be really strict in the diagnosis of FGPs (i.e. the presence of deep and superficial dilations). Infrequently, the two lesions may coexist. Foci of dysplasia can sometimes be seen.

A polyp is an abnormal growth of tissue projecting from a mucous membrane. If it is attached to the surface by a narrow elongated stalk, it is said to be "pedunculated". If no stalk is present, it is said to be "sessile". Polyps are commonly found in the colon, stomach, nose, ear, sinus(es), urinary bladder, and uterus. They may also occur elsewhere in the body where mucous membranes exist like the cervix, vocal folds, and small intestine. Some polyps are tumors (neoplasms) and others are nonneoplastic (for example, hyperplastic or dysplastic). The neoplastic ones are generally benign, although some can be premalignant and/or concurrent with a malignancy.

Age of onset is variable. The term 'Juvenile' in the title of Juvenile polyposis syndrome refers to the histological type of the polyps rather than age of onset.

Affected individuals may present with rectal bleeding, abdominal pain, diarrhea or anemia. On colonoscopy or sigmoidoscopy polyps that vary in shape or size are present. The polyps can be sessile or pedunculated hamartomatous polyps.

Juvenile polyposis syndrome is a syndrome characterized by the appearance of multiple juvenile polyps in the gastrointestinal tract. Polyps are abnormal growths arising from a mucous membrane. These usually begin appearing before age 20, but the term "juvenile" refers to the type of polyp, not to the age of the affected person. While the majority of the polyps found in Juvenile Polyposis Syndrome are non-neoplastic, hamartomatous, self-limiting and benign, there is an increased risk of adenocarcinoma.

Solitary juvenile polyps most commonly occur in the rectum and present with rectal bleeding. The World Health Organization criteria for diagnosis of juvenile polyposis syndrome are one of either:

1. More than five juvenile polyps in the colon or rectum; or

2. Juvenile polyps throughout the gastrointestinal tract; or

3. Any number of juvenile polyps in a person with a family history of juvenile polyposis.

A cervical polyp is a common benign polyp or tumor on the surface of the cervical canal. They can cause irregular menstrual bleeding or increased pain but often show no symptoms.

SSAs, generally, are asymptomatic. They are typically identified on a colonoscopy and excised for a definitive diagnosis and treatment.

Fundic gland polyposis is a medical syndrome where the fundus and the body of the stomach develop many polyps. The condition has been described both in patients with familial adenomatous polyposis (FAP) and attenuated variants (AFAP), and in patients in whom it occurs sporadically.

SSAs are diagnosed by their microscopic appearance; histomorphologically, they are characterized by (1) basal dilation of the crypts, (2) basal crypt serration, (3) crypts that run horizontal to the basement membrane (horizontal crypts), and (4) crypt branching. The most common of these features is basal dilation of the crypts.

Unlike traditional colonic adenomas (e.g. tubular adenoma, villous adenoma), they do not (typically) have nuclear changes (nuclear hyperchromatism, nuclear crowding, elliptical/cigar-shaped nuclei).

Most polyps do not cause noticeable symptoms. Gallbladder polyps are usually found incidentally when examining the abdomen by ultrasound for other conditions, usually abdominal pain.

Symptoms of polyps include nasal congestion, sinusitis, loss of smell, thick nasal discharge, facial pressure, nasal speech, and mouth breathing. Recurrent sinusitis can result from polyps. Long-term, nasal polyps can cause destruction of the nasal bones and widening of the nose.

As polyps grow larger, they eventually prolapse into the nasal cavity resulting in symptoms. The most prominent symptoms of nasal polyps result blockage of the nasal passage.

People with nasal polyps due to aspirin intolerance often have symptoms known as Samter's triad, which consists of asthma worse with aspirin, a skin rash caused by aspirin, and chronic nasal polyps.

Gallbladder polyps are growths or lesions resembling growths (polypoid lesions) in the wall of the gallbladder. True polyps are abnormal accumulations of mucous membrane tissue that would normally be shed by the body. The main types of polypoid growths of the gallbladder include cholesterol polyp/cholesterosis, cholesterosis with fibrous dysplasia of gallbladder, adenomyomatosis, hyperplastic cholecystosis, and adenocarcinoma.

Villous adenoma is a type of polyp that grows in the colon and other places in the gastrointestinal tract and sometimes in other parts of the body. These adenomas may become malignant (cancerous). Villous adenomas have been demonstrated to contain malignant portions in about one third of affected persons, and invasive malignancy in another one third of removed specimens. Colonic resection may be required for large lesions. These can also lead to secretory diarrhea with large volume liquid stools with few formed elements. They are commonly described as secreting large amounts of mucus, resulting in hypokalaemia in patients. On endoscopy a "cauliflower' like mass is described due to villi stretching. Being an adenoma, the mass is covered in columnar epithelial cells.

Nasal polyps (NP) are noncancerous growths within the nose or sinuses. Symptoms include trouble breathing through the nose, loss of smell, decreased taste, post nasal drip, and a runny nose. The growths are sac-like, movable, and nontender, though face pain may occasionally occur. They typically occur in both nostrils in those who are affected. Complications may include sinusitis and broadening of the nose.

The exact cause is unclear. They may be related to chronic inflammation of the lining of the sinuses. They occur more commonly among people who have allergies, cystic fibrosis, aspirin sensitivity, or certain infections. The polyp itself represents an overgrowth of the mucous membranes. Diagnosis may occur by looking up the nose. A CT scan may be used to determine the number of polyps and help plan surgery.

Treatment is typically with steroids, often in the form of a nasal spray. If this is not effective surgery may be considered. The condition often recurs following surgery, thus continued use of a steroid nasal sprays is often recommended. Antihistamines may help with symptoms but do not change the underlying disease. Antibiotics are not required for treatment unless an infection occurs.

About 4% of people currently have nasal polyps while up to 40% of people develop them at some point in their life. They most often occur after the age of 20 and are more frequent in males than females. Nasal polyps have been described since at least the time of the Ancient Egyptians.

Tubulovillous adenoma, TVA, is a type of polyp that grows in the colon and other places in the gastrointestinal tract and sometimes in other parts of the body. These adenomas may become malignant (cancerous).

TVAs are considered to have a higher risk of malignant transformation than tubular adenomas.

Inflammatory fibroid polyp, abbreviated IFP, is a benign abnormal growth of tissue projecting into the lumen of the gastrointestinal tract.

IFPs consist of spindle cells that are concentrically arranged around blood vessels and have inflammation, especially eosinophils.

They may have leiomyoma/schwannoma-like areas with nuclear palisading.

They typically stain with CD34 and vimentin, and, generally, do not stain with CD117 and S100.

The endoscopic differential diagnosis includes other benign, pre-malignant and malignant gastrointestinal polyps.

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.

Adenocarcinoma (; plural adenocarcinomas or adenocarcinomata ) is a type of cancerous tumor that can occur in several parts of the body. It is defined as neoplasia of epithelial tissue that has glandular origin, glandular characteristics, or both. Adenocarcinomas are part of the larger grouping of carcinomas, but are also sometimes called by more precise terms omitting the word, where these exist. Thus invasive ductal carcinoma, the most common form of breast cancer, is adenocarcinoma but does not use the term in its name—however, esophageal adenocarcinoma does to distinguish it from the other common type of esophageal cancer, esophageal squamous cell carcinoma. Several of the most common forms of cancer are adenocarcinomas, and the various sorts of adenocarcinoma vary greatly in all their aspects, so that few useful generalizations can be made about them.

In the most specific usage (narrowest sense), the glandular origin or traits are exocrine; endocrine gland tumors, such as a VIPoma, an insulinoma, or a pheochromocytoma, are typically not referred to as adenocarcinomas but rather are often called neuroendocrine tumors. Epithelial tissue sometimes includes, but is not limited to, the surface layer of skin, glands, and a variety of other tissue that lines the cavities and organs of the body. Epithelial tissue can be derived embryologically from any of the germ layers (ectoderm, endoderm, or mesoderm). To be classified as adenocarcinoma, the cells do not necessarily need to be part of a gland, as long as they have secretory properties. Adenocarcinoma is the malignant counterpart to adenoma, which is the benign form of such tumors. Sometimes adenomas transform into adenocarcinomas, but most do not.

Well differentiated adenocarcinomas tend to resemble the glandular tissue that they are derived from, while poorly differentiated adenocarcinomas may not. By staining the cells from a biopsy, a pathologist can determine whether the tumor is an adenocarcinoma or some other type of cancer. Adenocarcinomas can arise in many tissues of the body owing to the ubiquitous nature of glands within the body, and, more fundamentally, to the potency of epithelial cells. While each gland may not be secreting the same substance, as long as there is an exocrine function to the cell, it is considered glandular and its malignant form is therefore named adenocarcinoma.

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.

Bronchial adenomas are adenomas in the bronchi. They may cause carcinoid syndrome, a type of paraneoplastic syndrome.

Cervical polyps often show no symptoms. Where there are symptoms, they include intermenstrual bleeding, abnormally heavy menstrual bleeding (menorrhagia), vaginal bleeding in post-menopausal women, bleeding after sex and thick white vaginal or yellowish discharge (leukorrhoea).

A gastrointestinal carcinoid tumor is a rare, slow-growing form of cancer that affects certain cells in the lining of the stomach and intestines. The cells it affects make hormones that regulate the production of digestive juices and muscles that move food through the stomach and intestines. This kind of cancer usually occurs in the appendix, small intestine, or rectum. Its presence is associated with an increased risk of cancers affecting the other parts of the digestive system. It is usually treated with surgery.

A benign tumor is a mass of cells (tumor) that lacks the ability to invade neighboring tissue or metastasize. Benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually do not grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening. Benign tumors generally have a slower growth rate than malignant tumors and the tumor cells are usually more differentiated (cells have normal features). Benign tumors are typically surrounded by an outer surface (fibrous sheath of connective tissue) or remain with the epithelium. Common examples of benign tumors include moles and uterine fibroids.

Although benign tumors will not metastasize or locally invade tissues, some types may still produce negative health effects. The growth of benign tumors produces a "mass effect" that can compress tissues and may cause nerve damage, reduction of blood to an area of the body (ischaemia), tissue death (necrosis) and organ damage. The mass effect of tumors is more prominent if the tumor is within an enclosed space such as the cranium, respiratory tract, sinus or inside bones. Tumors of endocrine tissues may overproduce certain hormones, especially when the cells are well differentiated. Examples include thyroid adenomas and adrenocortical adenomas.

Although most benign tumors are not life-threatening, many types of benign tumors have the potential to become cancerous (malignant) through a process known as tumour progression. For this reason and other possible negative health effects, some benign tumors are removed by surgery.