• Small intestinal carcinoid: The most common presentation of this disease is the abdominal pain caused by fibrosis of the mesentery, or intestinal obstruction.
• Ectopic adenocorticotropic hormone (ACTH) and Cushing’s disease: These symptoms are observed in foregut carcinoid tumors and must be differentiated with that observed in other tumors. Carcinoid tumors can cause rare acromegaly, which must be differentiated from pituitary tumors.
• Carcinoid crisis: The symptoms such as intense flushing, diarrhea, tachycardia, hyper- or hypotension can happen spontaneously in carcinoid tumors or as a response to chemotherapy or anesthesia.
• Cutaneous flushing: In 94% of the cases, the symptom of carcinoid tumors is cutaneous flushing, which affects the head and neck. Some of the triggers of the flushing are exercise, stress and some food.
• Most of the patients with carcinoid tumor suffer from diarrhea and malabsorption. In these patients, the stool is frothy, watery and bulky.
• Asthma-like syndrome or wheezing is caused by the constriction of the bronchi. There are some tremors which are relatively indolent resulting in chronic symptoms such as cough and shortness of breath.
• Valvular heart lesions, fibrosis of endocardium on the right side is observed in such patients, though pulmonic valve fibrosis is relatively uncommon. Lesion on the cardiac tissues can cause heart failure.
• Often carcinoid tumors occur in association with the genetic disorders such as multiple endocrine neoplasia type I and Peutz-Jeghers syndrome.
• In carcinoid tumor, multicentric tumors in more than one organ have been reported [1] [4].

Laboratory studies

Diagnosis of carcinoid tumors depends on the characteristic biomarker of the disease. Measuring the biogenic amine (such as serotonin, histamine, and catecholamines) levels as well their metabolites in the plasma is important to diagnose the carcinoid tumor.

• Urinary 5-HIAA levels: The increased levels of 5-HIAA in the urine helps in the assessment of carcinoid tumors. These levels, though, may not help in the detection of tumors at the early stage.
• Fasting plasma 5-HIAA assay: This is a more stable and convenient test.
• CDX2 and TTF-1 are indicative of the GI carcinoid tumors and pulmonary tumors respectively.

Imaging

Imaging techniques that can diagnose carcinoid tumors are as follows:

• Upper and lower gastrointestinal tract radiography
• CT
• MRI
• MIBG (metaiodobenzylguanidine) scan
• PET

Depending on the type and location of the tumor, a combination of either of these can be used. For chest tumors, CT along with scintigraphy is used. Large bowel disease is often diagnosed by colonoscopy. Mesenteric invasion and liver metastasis can be detected by CT scans. For hepatic disease, MRI can be helpful in the diagnosis of the condition. PET scanning is helpful for the diagnosis and follow-up of the tumors. Radionuclide imaging has proven to be the best diagnostic tool for the diagnosis of carcinoid tumors. Somatostatin-receptor scintigraphy (SRS) and CT scanning can help detect localized tumors [1] [5] [6].

Medical care: In case where the surgical excision is not suitable in patients with carcinoid tumor, the following chemotherapy drugs are recommended. Alkylating agents, doxorubicin, actinomycin D, cisplatin, interferon-alfa and streptozocin are some of the drugs that are used to manage the condition. In most of the cases, a combination of the agents is used.

Chemoembolization is one of the strategies for the management of carcinoid tumors. Though octreotide has been found to be very effective in reducing the symptoms, its use in pediatric population is still debated, as it reduces the level of growth factor which is produced impairing growth [7] [8].

Surgical care: The surgical excision as a treatment choice depends on the feasibility of the condition. Surgical technique depends on the location and the stage of the tumor. Simple appendectomy is the treatment option in most of the cases.

Block resection of the tumor (with the adjacent lymph nodes) is a surgical treatment adopted for intestinal carcinoids, while in case of bronchial tumor, surgical resection is opted. In most of the localized tumor, surgical resection works. For managing rectal tumor, endoscopic resection is sufficient. Debulking can provide symptomatic relief in patients when total resection is not possible [9] [10] [11].

Prognosis in the patients with carcinoid tumors depends on some important factors such as the location and size of the tumor, if the tumor has spread to other parts of the body, or if the tumor can be removed completely by surgery or if it recurred or was diagnosed for the first time.

Complications

Carcinoid tumors secrete chemicals which can lead to complications such as carcinoid syndrome (skin flushing, chronic diarrhea, problems in breathing), carcinoid heart disease (leaky heart valves, and heart failure) and Cushing syndrome.

Though the etiology of the carcinoid tumor is not known, genetic abnormalities are often suspected. Changes in the chromosomal abnormalities can be defined as the loss of heterogeneity or numerical alterations of the chromosomes [1].

Carcinoids are the most common neuroendocrine tumors. The true incidence of this type of tumor is still not clear. Though it is estimated to be around 1 every 100,000 individuals, there are some studies that have shown necropsies in approximately 1% of the population [2].

The carcinoid tumors are of neuroendocrine origin. These tumors are derived from the primitive stem cells, giving rise to the multiple cell lineages. These tumors develop in the mucosa of the intestinal tract and grow slowly, extending to the submucosa and mucosal surface, resulting in the formation of small nodules.

The tumors are yellow, or gray-brown in color, due to the accumulation of cholesterol and lipids. Metastases can also occur in the liver, spleen, peritoneum, liver and the ovaries. Five distinct patterns of the carcinoid tumors are observed upon histological examination.

Some of the products of the carcinoid tumors are amylin, dopamine, gastrin, bombesin, catecholamines, motilin, pancreatic polypeptide, prostaglandins, serotonin, somatostatin and substance-P. The carcinoid tumors are found to be argyrophilic and argentaffinic, with somatostatin receptors. There is a high potential for metastasis in carcinoid tumors as these cells produce betacatenin [1] [3].

Though carcinoid tumor has a genetic component, the risk of such tumors can reduce by taking some of the steps:

• Maintaining a healthy bodyweight 
• Regular exercises
• Annual screening of such tumors
• Quit smoking

Carcinoid tumors are derived from primitive stem cells, present in the gut wall, and other organs such as thymus, lungs, liver, ovaries, prostate and kidneys. Among children, carcinoid tumors are seen in the appendix which are benign and asymptomatic.

Most of these tumors are slow-growing and asymptomatic, though some are aggressive and metastatic. Carcinoid tumors can be classified based on the location of the primitive gut giving rise to the tumor such as foregut, midgut and hindgut.

Meckel diverticulum, mesentry and cystic duplications can also lead to the development of carcinoid tumors. These entities have shown distinctive features: clinical, histochemical, and secretory. While both foregut and hindgut carcinoids are argentaffin negative, the midgut carcinoids are argentaffin positive. Foregut tumors can metastasize to the bone and can be associated with acromegaly, Cushing’s disease, and hypertrophy of the skin of the face and the upper neck. In midgut and hindgut carcinoids, the bone metastasis is uncommon, though midgut carcinoid tumors have the rare potential to produce the corticotropic hormone [1].

Carcinoid tumors are derived from primitive stem cells, present in the gut wall, and other organs such as thymus, lungs, liver, ovaries, prostate and kidneys. There are no specific symptoms of the disease, however since there is a genetic component in the pathogenesis of the disease, any family member diagnosed earlier with carcinoid tumor adds to the risk of this disease in the sibling or children. Hence, in such cases, the patient must not neglect any possible signs and symptoms.

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