Gastrointestinal Neuroendocrine Tumors (GI NET)


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Endocrine Surgeons

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UW Health endocrine surgeons treat the following kinds of gastrointestinal neuroendocrine tumors (GI NET).
Insulinomas are the most common type of NET. They occur more commonly in females in the fifth or sixth decade. These tumors secrete insulin or less commonly proinsulin which lead to the clinical syndrome of hypoglycemic symptoms, low blood glucose, and relief with administration of glucose, referred to as Whipple's triad.
These symptoms are often exacerbated with fasting and relieved by food consumption. The majority of insulinomas are small (< 2cm), solitary, benign (>90 percent) and uniformly distributed throughout the pancreas.
The most sensitive imaging technique is intraoperative ultrasound, which localizes over 90 percent of insulinomas. Therefore, after the biochemical diagnosis of insulinoma is made, we usually obtain a CT scan and, if negative, an endoscopic ultrasound. Even if the lesion does not localize, we would still proceed to the operating room and perform intraoperative palpation and ultrasound for localization.
The treatment of choice for insulinoma is complete resection of the tumor. Because the vast majority of insulinomas are benign, enucleation is performed when possible.
Gastrinoma (Zollinger-Ellison Syndrome)
Gastrinomas are the second most common type of pancreatic NE tumor and occur in 0.1-1 percent of all patients with peptic ulcer disease. They occur more commonly in males and usually in the sixth or seventh decade. About 75 percent occur sporadically while 25 percent are associated with the MEN-1 syndrome.
Sixty percent of gastrinomas are located within the pancreas and 30 percent are located within the duodenum. In contrast to insulinomas, most gastrinomas are malignant (60 percent). Gastrinomas are very small and CT, transabdominal ultrasound, and MRI only detect  less than 50 percent of lesions. Octreotide scanning has a reported sensitivity of 80-90 percent and when combined with endoscopic ultrasound will detect over 90 percent of all gastrinomas. Similar to insulinomas, gastrinomas not detected pre-operatively can be usually found at the time of surgery with intraoperative palpation and ultrasound.
As with all NETs, the only chance for complete cure of gastrinoma is surgical resection.
Pancreatic Polypeptide-Secreting Tumor (Ppoma)
The third most common type of islet cell tumor is a PPoma. The function of pancreatic polypeptide is not completely understood. Patients present with weight loss, jaundice, and abdominal pain.
PPomas tend to be large by the time of diagnosis and are usually seen in CT or MRI. Octreotide scanning is also sensitive for the detection of these tumors. Surgical resection is the only chance for cure for those patients without widely metastatic disease. Since many of these tumors are large and located in the pancreatic head, ampulla, or duodenum when diagnosed, a pancreaticoduodenectomy may be needed.
Patients typically present in the fifth decade of life with an even gender distribution. Hepatic metastases have been reported in more than 50 percent of patients at the time of diagnosis. Glucagonomas are very rare tumors that cause the "4D syndrome": diabetes, dermatitis, deep vein thrombosis, and depression. Additional findings associated with glucagonoma include cheilitis, anemia, weight loss, hypoaminoacidemia, and other neuropsychiatric symptoms.
Patient often present with elevated glucose and a characteristic rash called necrolytic migratory erythema seen in the face, lower abdomen, perineum, and lower extremities. Skin biopsy can occasionally confirm the diagnosis. 
Glucagonomas tend to be solitary and are more commonly occur in the body and tail of the pancreas. A distal pancreatectomy is usually the operation of choice for these tumors without evidence for metastatic disease; however, enucleation, partial resection, and pancreaticoduodenectomy have all been described and are appropriate options based on the location of the tumor.
Vasoactive Intestinal Peptide-Secreting Tumor (VIPoma)
VIPomas are also extremely rare tumors that cause the "WDHA syndrome": watery (secretory) diarrhea, hypokalemia, and achlorhydria. Other symptoms include abdominal pain, flushing, muscle weakness, and weight loss and can often been mistaken for carcinoid syndrome.
These rare tumors occur with a frequency of 1 per 10,000,000 per year. These tumors arise in the pancreas 90 percent of the time, but have also been described in the colon, bronchus, adrenals, liver, and sympathetic ganglia. Adults typically present between ages 30 and 50 years. VIPomas are typically solitary and greater than three centimeters in diameter, with 75 percent located in the tail of the pancreas.
The majority of VIPomas can be localized with CT or MRI. Octreotide scanning is also highly sensitive. Sixty to eighty percent are metastatic at the time of diagnosis. The first course of action once VIPoma has been diagnosed is to aggressively correct the dehydration and metabolic derangements intrinsic to the syndrome. Octreotide can stop the diarrhea and allow for the correction of hypokalemia and other metabolic abnormalities in the majority of these patients. Occasionally, enucleation can be performed but resection often consists of a distal pancreatectomy.
Somatostatinomas are the rarest pancreatic NE tumor. Patients present with symptoms such as abdominal pain, weight loss, steatorrhea, hyperglycemia, and cholelithiasis.
The median age at diagnosis is 50, and gender distribution is equal. Most somatostatinomas are solitary. Fifty-six to seventy percent of these tumors are located in the pancreas. Two-thirds of pancreatic somatostatinomas are located in the head of the pancreas. Most of the extrapancreatic tumors are located in the duodenum, ampulla, or remaining small bowel.
Somatostatinomas often go undiagnosed for years and therefore very large (> 5cm) at the time of presentation. The majority of somatostatinomas are metastatic are presentation (90 percent) and can be localized with CT or MRI. Octreotide scanning is also highly sensitive. Most somatostatinomas require a pancreaticoduodenectomy for resection.
Non-Functional Islet Cell Tumors
Non-functional islet cell tumors histologically resemble other NETs but do not secrete biologically active substances that result in a detectable clinical syndrome. Most likely, they either secrete low levels of hormones, biologically inactive hormones or hormones that are presently unidentified. Most of these tumors, however, secrete chromogranin A which can be detected in the serum and thus confirm the diagnosis.
Most patients present with abdominal pain or other vague symptoms prompting diagnostic studies. Almost all of non-functional islet cell tumors are diagnosed by CT or MRI due to the lack of symptomatology. The tumors are very large at the time of presentation (>6cm) and  more than 50 percent are malignant. Most non-functional islet cell tumors arise in the pancreatic head and require a pancreaticoduodenectomy for resection.
Carcinoid Tumors
Carcinoids are derived from Kulchinsky or enterochromaffin cells, which are part of the diffuse neuroendocrine cells of the gut. The incidence of carcinoid tumors is estimated to be one to two cases per 100,000 people, accounting for just 0.5 percent of all malignancies.
The diagnosis of a carcinoid tumor is based on histology with confirmation by immunohistochemical staining with neuroendocrine markers. Serotonin is the most commonly secreted substance and can cause the symptoms of the classic "carcinoid syndrome," consisting of flushing, diarrhea, bronchoconstriction, and ultimately valvular heart disease.
Unfortunately, histologic examination cannot predict the aggressiveness or metastatic potential of carcinoid tumors. Malignancy is based upon the presence of metastatic disease. The most common sites of metastases are the lymph nodes, liver, and less frequently bone. The prognosis of carcinoid tumors varies greatly depending on the location of the tumor and the extent of spread at the time of diagnosis.
Pulmonary Carcinoid Tumors
Pulmonary carcinoids account for 2 percent of primary lung tumors and about 25 percent of all carcinoid tumors.
Two-thirds of pulmonary carcinoids are considered typical, are found in a perihilar location, and most commonly present in the fifth decade. The carcinoid syndrome occurs in less than 5 percent of these patients, with more common symptoms being recurrent pneumonia, cough, hemoptysis, or chest pain.
Atypical carcinoids typically occur in the periphery of the lungs and arise in older patients. Their course is more aggressive with up to 50 percent having lymph node metastasis, leading to a 5-year survival of only 40-75 percent.
Gastric Carcinoid Tumors
Type 1 gastric carcinoids are the most frequent, accounting for 63-75 percent of cases. These tumors develop in patients with type A chronic atrophic gastritis (CAG-A) and are believed to be due to overproduction of gastrin in these patients. These tumors tend to be non-functional and asymptomatic. Type 1 gastric carcinoid tumors rarely metastasize.
Type 2 gastric carcinoids are rare (0-10 percent) and arise in the setting of Multiple Endocrine Neoplasia 1 and Zollinger-Ellison syndrome. These tumors are often multiple and display a low grade of malignant behavior. Hypergastrinemia plays an important role in stimulating the growth of both Type 1 and 2 gastric carcinoids, although hypergastrinemia alone is not believed to be causative.
Type 3 gastric carcinoids are the sporadic variety which accounts for 13-20 percent of tumors. Gastric carcinoids may cause an atypical carcinoid syndrome: flushing, hypotension, lacrimation, edema, and bronchoconstriction or may secrete adrenocorticotropic hormone (ACTH).
Small Intestinal Carcinoid Tumors
The most common location for carcinoid tumors is the small bowel (29 percent), with over half being in the distal ileum. Patients typically present with symptoms of abdominal pain or intestinal obstruction. These lesions may cause kinking of the bowel leading to intermittent obstruction or intestinal ischemia.
These tumors tend to be slow growing and have a prolonged disease course. The classic carcinoid syndrome is present in only 5 percent of patients. The majority of these lesions have spread to the lymph nodes (39 percent) or have distant metastases (31 percent) at the time of diagnosis. The five-year survival is 65 percent with localized/regional disease, but falls to 36 percent when distant disease is present.
Appendiceal Carcinoid Tumors
The majority of appendiceal carcinoids are diagnosed incidentally during surgery. Over half of patients with appendiceal carcinoids present with signs and symptoms suggestive of acute appendicitis. The prognosis of appendiceal carcinoids is very good. The five-year survival is 94 percent for local disease, 85 percent for regional metastasis, and 34 percent when distant metastases are present.
Colonic Carcinoid Tumors
Colonic carcinoid tumors are rare and typically present during the seventh decade of life. These tumors are more frequent in women and are often symptomatic at the time of diagnosis, with abdominal pain being the most common complaint. These tumors tend to be large and are most commonly located in the right colon.
At the time of diagnosis, approximately 44 percent have spread to the lymph nodes and 38 percent have spread to distant locations. The overall five-year survival of these lesions is 25-41 percent.
Rectal Carcinoid Tumors
About 50 percent of these tumors are diagnosed incidentally on routine endoscopy. The size of these tumors is closely correlated to their risk of metastasis as well as their survival. The five-year survival rates for these patients is 81 percent if there is only local disease, 47 percent if regional metastasis are present, and 18 percent if distant metastases are found.