The most common presentation is gastrointestinal bleed (~45% of cases), followed by abdominal pain (~43% of cases) and anemia (~15% of cases).

GP consist of three components (1) ganglion cells, (2) epithelioid cells (neuroendocrine-like), and (3) spindle cells (schwannoma-like). The microscopic differential diagnosis includes poorly differentiated carcinoma, neuroendocrine tumour and paraganglioma.

GPs may be sporadic or arise in the context neurofibromatosis type 1.

Carney triad (CT) is characterized by the coexistence of three types of neoplasms, mainly in young women, including gastric gastrointestinal stromal tumor, pulmonary chondroma, and extra-adrenal paraganglioma. The underlying genetic defect remains elusive. CT is distinct from Carney complex, and the Carney-Stratakis syndrome.

The strumal carcinoid is a type of monodermal teratoma with histomorphologic features of (1) the thyroid gland and (2) a neuroendocrine tumour (carcinoid).

Ceruminous adenoma are rare tumors, accounting for less than 1% of all external ear tumors. The patients will present with a mass, perhaps associated pain, and may have changes in hearing (usually a sensorineural or a conductive hearing loss). Some patients have tinnitus. Nerve paralysis is very uncommon.

Glomus tumors are usually solitary and small lesions. The vast majority are found in the distal extremities, particularly in the hand, wrist, foot, and under the fingernails.

They are often painful, and the pain is reproduced when the lesion is placed in cold water.

These tumors tend to have a bluish discoloration, although a whitish appearance may also be noted. Elevation of the nail bed can occur.

In rare cases, the tumors may present in other body areas, such as the gastric antrum or glans penis. Treatment is essentially the same.

The exact incidence of glomus tumors is unknown. The multiple variant is rare, accounting for less than 10% of all cases. The probable misdiagnosis of many of these lesions as hemangiomas or venous malformations also makes an accurate assessment of incidence difficult.

- Sex:

Solitary glomus tumors, particularly subungual lesions, are more common in females than in males. Multiple lesions are slightly more common in males.

- Age:

Solitary glomus tumors are more frequent in adults than in others. Multiple glomus tumors develop 11–15 years earlier than single lesions; about one third of the cases of multiple tumors occur in those younger than 20 years. Congenital glomus tumors are rare; they are plaquelike in appearance and are considered a variant of multiple glomus tumors.

Hyperparathyroidism is present in ≥ 90% of patients. Asymptomatic hypercalcemia is the most common manifestation: about 25% of patients have evidence of nephrolithiasis or nephrocalcinosis. In contrast to sporadic cases of hyperparathyroidism, diffuse hyperplasia or multiple adenomas are more common than solitary adenomas.

Pain is the most common symptom, followed by either sensorineural or conductive hearing loss, tinnitus or drainage (discharge). A mass lesion may be present, but it is often slow growing.

The classical LFS malignancies - sarcoma, cancers of the breast, brain and adrenal glands - comprise about 80% of all cancers that occur in this syndrome.

The risk of developing any invasive cancer (excluding skin cancer) is ~50% by age 30 (1% in the general population) and is 90% by age 70. Early onset breast cancer accounts for 25% of all the cancers in this syndrome. This is followed by soft tissue sarcomas (20%), bone sarcoma (15%) and brain tumors - especially glioblastomas - (13%). Other tumours seen in this syndrome include leukemia, lymphoma and adrenocortical carcinoma.

~90% of females with LFS develop breast cancer by age 60 years; the majority of these occur before age 45 years. Females with this syndrome have almost a 100% lifetime risk of developing cancer. This compares with 73% for affected males. The difference may be due to much smaller breast tissue in males as well as increased estrogen levels in females.

The risks of sarcoma, female breast cancer and haematopoietic malignancies in mutation carriers are more than 100 times greater than those seen in the general population.

Other tumours reported in this syndrome but not yet proved to be linked with it include melanoma, Wilm's and other kidney tumors, hepatacellular carcinoma, gonadal germ cell, pancreatic, gastric, choroid plexus, colorectal and prostate cancers.

80% of children with adrenocortical carcinoma and 2%-10% of childhood brain tumors have p53 mutations.

2%-3% of osteosarcomas, 9% rhabdomyosarcomas and 7%-20% patients with multiple primary tumors have p53 mutations.

Although most cases of this syndrome have early onset of cancer, cases have also been reported later in life.

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.

While most carcinoids are asymptomatic through the natural lifetime and are discovered only upon surgery for unrelated reasons (so-called "coincidental carcinoids"), all carcinoids are considered to have malignant potential.

About 10% of carcinoids secrete excessive levels of a range of hormones, most notably serotonin (5-HT), causing:

- Flushing (serotonin itself does not cause flushing). Potential causes of flushing in carcinoid syndrome include bradykinins, prostaglandins, tachykinins, substance P, and/or histamine, diarrhea, and heart problems. Because of serotonin's growth-promoting effect on cardiac myocytes,[14] a serotonin-secreting carcinoid tumour may cause a tricuspid valve disease syndrome, due to the proliferation of myocytes onto the valve.

- Diarrhea

- Wheezing

- Abdominal cramping

- Peripheral edema

The outflow of serotonin can cause a depletion of tryptophan leading to niacin deficiency. Niacin deficiency, also known as pellagra, is associated with dermatitis, dementia, and diarrhea.

This constellation of symptoms is called "carcinoid syndrome" or (if acute) "carcinoid crisis". Occasionally, haemorrhage or the effects of tumor bulk are the presenting symptoms. The most common originating sites of carcinoid is the small bowel, particularly the ileum; carcinoid tumors are the most common malignancy of the appendix. Carcinoid tumors may rarely arise from the ovary or thymus.

They are most commonly found in the midgut at the level of the ileum or in the appendix. The next most common affected area is the respiratory tract, with 28% of all cases — per PAN-SEER data (1973 – 1999). The rectum is also a common site.

Pancreatic islet cell tumors occur in 60 to 70% of patients. Tumors are usually multicentric. Multiple adenomas or diffuse islet cell hyperplasia commonly occurs; such tumors may arise from the small bowel rather than the pancreas. About 30% of tumors are malignant and have local or distant metastases. Malignant islet cell tumors due to MEN 1 syndrome often have a more benign course than do sporadically occurring malignant islet cell tumors.About 40% of islet cell tumors originate from a β-cell, secrete insulin (insulinoma), and can cause fasting hypoglycemia. β-cell tumors are more common in patients 40 years of age. Non-β-cell tumors are somewhat more likely to be malignant.

Most islet cell tumors secrete pancreatic polypeptide, the clinical significance of which is unknown. Gastrin is secreted by many non–β-cell tumors (increased gastrin secretion in MEN 1 also often originates from the duodenum). Increased gastrin secretion increases gastric acid, which may inactivate pancreatic lipase, leading to diarrhea and steatorrhea. Increased gastrin secretion also leads to peptic ulcers in > 50% of MEN 1 patients. Usually the ulcers are multiple or atypical in location, and often bleed, perforate, or become obstructed. Peptic ulcer disease may be intractable and complicated. Among patients presenting with Zollinger-Ellison syndrome, 20 to 60% have MEN 1.

A severe secretory diarrhea can develop and cause fluid and electrolyte depletion with non–β-cell tumors. This complex, referred to as the watery diarrhea, hypokalemia and achlorhydria syndrome (VIPoma) has been ascribed to vasoactive intestinal polypeptide, although other intestinal hormones or secretagogues (including prostaglandins) may contribute. Hypersecretion of glucagon, somatostatin, chromogranin, or calcitonin, ectopic secretion of ACTH resulting in Cushing's syndrome, and hypersecretion of somatotropin–releasing hormone (causing acromegaly) sometimes occur in non–β-cell tumors. All of these are rare in MEN 1.Nonfunctioning pancreatic tumors also occur in patients with MEN 1 and may be the most common type of pancreatoduodenal tumor in MEN 1. The size of the nonfunctioning tumor correlates with risk of metastasis and death.

The most common adverse effect is pain, which is usually associated with solitary lesions. Multiple tumors are less likely to be painful.

In one report, a patient with more than 400 glomus tumors had thrombocytopenia as a result of platelet sequestration (i.e. Kasabach-Merritt syndrome).

Malignant glomus tumors, or glomangiosarcomas, are extremely rare and usually represent a locally infiltrative malignancy. However, metastases do occur and are usually fatal.

GCCs have an aggressive course compared to other appendiceal neuroendocrine tumours.

Most paragangliomas are either asymptomatic or present as a painless mass. While all contain neurosecretory granules, only in 1–3% of cases is secretion of hormones such as catecholamines abundant enough to be clinically significant; in that case manifestations often resemble those of pheochromocytomas (intra-medullary paraganglioma).

This tumor only affects the outer 1/3 to 1/2 of the external auditory canal as a primary site. If this area is not involved, the diagnosis should be questioned. The most common tumor type is ceruminous adenoid cystic carcinoma and ceruminous adenocarcinoma, NOS.

The World Health Organization (WHO) classification scheme places neuroendocrine tumors into three main categories, which emphasize the tumor grade rather than the anatomical origin:

- well-differentiated neuroendocrine tumours, further subdivided into tumors with benign and those with uncertain behavior

- well-differentiated (low grade) neuroendocrine carcinomas with low-grade malignant behavior

- poorly differentiated (high grade) neuroendocrine carcinomas, which are the large cell neuroendocrine and small cell carcinomas.

Additionally, the WHO scheme recognizes mixed tumors with both neuroendocrine and epithelial carcinoma features, such as goblet cell cancer, a rare gastrointestinal tract tumor.

Placing a given tumor into one of categories depends on well-defined histological features: size, lymphovascular invasion, mitotic counts, Ki-67 labelling index, invasion of adjacent organs, presence of metastases and whether they produce hormones.

GCCs are diagnosed by pathology. They have a characteristic biphasic appearance which includes (1) goblet cell-like cells, and (2) neuroendocrine-type nuclear chromatin (stippled chromatin).

Neuroendocrine adenoma of the middle ear (NAME) is a tumor which arises from a specific anatomic site: middle ear. NAME is a benign glandular neoplasm of middle ear showing histologic and immunohistochemical neuroendocrine and mucin-secreting differentiation (biphasic or dual differentiation).

About 85% of paragangliomas develop in the abdomen; only 12% develop in the chest and 3% in the head and neck region (the latter are the most likely to be symptomatic). While most are single, rare multiple cases occur (usually in a hereditary syndrome). Paragangliomas are described by their site of origin and are often given special names:

- Carotid paraganglioma (carotid body tumor): Is the most common of the head and neck paragangliomas. It usually presents as a painless neck mass, but larger tumors may cause cranial nerve palsies, usually of the vagus nerve and hypoglossal nerve.

- Organ of Zuckerkandl: A collection of paraganglia near the bifurcation of the aorta, comprising a small mass of neural crest-derived chromaffin cells. Serves as a common origin of abdominal paragangliomas.

- Glomus tympanicum and Glomus jugulare: Both commonly present as a middle ear mass resulting in tinnitus (in 80%) and hearing loss (in 60%). The cranial nerves of the jugular foramen may be compressed, resulting swallowing difficulty, or ipsilateral weakness of the upper trapezius and sternocleiodomastoid muscles (from compression of the spinal accessory nerve). These patients present with a reddish bulge behind an intact ear drum. This condition is also known as the "Red drum". On application of pressure to the external ear canal with the help of a pneumatic ear speculum the mass could be seen to blanch. This sign is known as "Brown's sign". A deficient bony plate along the tympanic portion of the internal carotid artery (aberrant ICA) is a normal variant and can be mistaken with glomus jugulare.

- Vagal paraganglioma: These are the least common of the head and neck paragangliomas. They usually present as a painless neck mass, but may result in dysphagia and hoarseness.

- Pulmonary paraganglioma: These occur in the lung and may be either single or multiple.

- Other sites: Rare sites of involvement are the larynx, nasal cavity, paranasal sinuses, thyroid gland, and the thoracic inlet, as well as the bladder in extremely rare cases.

GISTs may present with trouble swallowing, gastrointestinal bleeding, or metastases (mainly in the liver). Intestinal obstruction is rare, due to the tumor's outward pattern of growth. Often, there is a history of vague abdominal pain or discomfort, and the tumor has become rather large by time the diagnosis is made.

This uncommon tumor accounts for less than 2% of all ear tumors. While patients present with symptoms related to the middle ear cavity location of the tumor, the tumor may expand into the adjacent structures (external auditory canal, mastoid bone, and eustachian tube). Patients come to clinical attention with unilateral (one sided) hearing loss, usually associated with decreased auditory acuity, and particularly conductive hearing loss if the ossicular bone chain (middle ear bones) is involved. Tinnitus (ringing), otitis media, pressure or occasionally ear discharge are seen. At the time of otoscopic exam, the tympanic membrane is usually intact, with a fluid level or mass noted behind the ear drum. Even though this is a "neuroendocrine" type tumor, there is almost never evidence of neuroendocrine function clinically or by laboratory examination.

A ceruminous adenoma (also known as adenoma of the ceruminous gland and ceruminoma) is a benign glandular neoplasm which arises from the ceruminous glands located within the external auditory canal. These glands are found within the outer one third to one half of the external auditory canal, more common along the posterior surface; therefore, the tumor develops within a very specific location.

Some PanNETs do not cause any symptoms, in which case they may be discovered incidentally on a CT scan performed for a different purpose. Symptoms such as abdominal or back pain or pressure, diarrhea, indigestion, or yellowing of the skin and whites of the eyes can arise from the effects of a larger PanNET tumor, either locally or at a metastasis. About 40% of PanNETS have symptoms related to excessive secretion of hormones or active polypeptides and are accordingly labeled as "functional"; the symptoms reflect the type of hormone secreted, as discussed below. Up to 60% of PanNETs are nonsecretory or nonfunctional, in which there is no secretion, or the quantity or type of products, such as pancreatic polypeptide (PPoma), chromogranin A, and neurotensin, do not cause a clinical syndrome although blood levels may be elevated. In total, 85% of PanNETs have an elevated blood marker.

Functional tumors are often classified by the hormone most strongly secreted, for example:

- gastrinoma: the excessive gastrin causes Zollinger–Ellison syndrome (ZES) with peptic ulcers and diarrhea

- insulinoma: hypoglycemia occurs with concurrent elevations of insulin, proinsulin and C peptide

- glucagonoma: the symptoms are not all due to glucagon elevations, and include a rash, sore mouth, altered bowel habits, venous thrombosis, and high blood glucose levels

- VIPoma, producing excessive vasoactive intestinal peptide, which may cause profound chronic watery diarrhea and resultant dehydration, hypokalemia, and achlorhydria (WDHA or pancreatic cholera syndrome)

- somatostatinoma: these rare tumors are associated with elevated blood glucose levels, achlorhydria, cholelithiasis, and diarrhea

- less common types include ACTHoma, CRHoma, calcitoninoma, GHRHoma, GRFoma, and parathyroid hormone–related peptide tumor

In these various types of functional tumors, the frequency of malignancy and the survival prognosis have been estimated dissimilarly, but a pertinent accessible summary is available.

The Carney complex is a distinct entity, characterized by myxomatous neoplasms (cardiac, endocrine, cutaneous and neural), and a host of pigmented lesions of the skin and mucosae, including the rarely occurring epitheloid blue nevus.