Glucagonoma pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Parminder Dhingra, M.D. [2] Mohammed Abdelwahed M.D[3]

Glucagonoma is a tumor of the alpha cells of the pancreas characterized by the excessive secretion of glucagon and necrolytic migratory erythema. Glucagonoma causes hyperglucagonemia, zinc deficiency, fatty acid deficiency, hypoaminoacidemia that may cause necrolytic migratory erythema. Glucagonoma may be a part of type 1 multiple endocrine neoplasia. It is an autosomal dominant syndrome that is usually caused by mutations in the MEN1 gene. MEN1 gene is a tumor suppressor gene and causes type 1 multiple endocrine neoplasia by Knudson’s “two hits” model for tumor development. All glucagonomas are located in the pancreas, 50–80% occur in the pancreatic tail, 32.2% in the body and 21.9% in the head. Glucagonoma can metastasize mainly to the liver. Glucagonomas consist of pleomorphic cells containing granules that stain for other peptides, most frequently pancreatic polypeptide. Immunoperoxidase staining can detect glucagon within the tumor cells and glucagon.

• Glucagonoma is a rare tumor of the alpha cells of the pancreas that results in the overproduction of the hormone glucagon. Glucagonomas are neuroendocrine tumors derived from multipotential stem cells.^{[1][2][3][4][5][6]}
  • Glucagon increases glycogenolysis, gluconeogenesis from amino acid substrates and inhibits glycolysis. This causes weight loss due to the catabolic action of glucagon.
  • When glucagon is secreted by a tumor, it becomes independent and is no longer influenced by feedback control mechanisms.
  • Glucagonoma causes hyperglucagonemia, zinc deficiency, fatty acid deficiency, hypoaminoacidemia that may cause necrolytic migratory erythema.
  • The mechanism for necrolytic migratory erythema involves excessive inflammation in the epidermis in response to trauma and to the necrolysis.
  • Necrolytic migratory erythema (NME) probably results from hyponutrition and amino acid deficiency. It can be caused by the loss of tryptophan in cutaneous tissues as a result of the excess circulating glucagon. Tryptophan is responsible for niacin function, which regulates cell turnover and the maturation of the epidermis and mucosal epithelia.
  • Diarrhea may result from the secretion of gastrin which occurs with glucagonoma.

Glucagonoma may be part of type 1 multiple endocrine neoplasia. It is an autosomal dominant syndrome that is usually caused by mutations in the MEN1 gene.^{[1][2][3][4][5][6][7]}

• It is characterized by the development of the following tumors:
  • Pituitary adenomas
  • Islet cell tumors of the pancreas (commonly gastrinoma and glucagonoma)
  • Parathyroid hyperplasia with resulting hyperparathyroidism
• The gene locus causing multiple endocrine neoplasia type 1 has been localized to chromosome 11q13 by studies of loss of heterozygosity on multiple endocrine neoplasia type 1-associated tumors and by linkage analysis in multiple endocrine neoplasia type 1 families. MEN1, spans about 10 Kb and consists of ten exons encoding a 610 amino acid nuclear protein, named menin.
• MEN1 gene is a tumor suppressor gene and causes type 1 multiple endocrine neoplasia by Knudson’s “two hits” model for tumor development.
• Two hits model for tumor development suggests that there is a germline mutation present in all cells at birth and the second mutation is a somatic mutation that occurs in the predisposed endocrine cell and leads to loss of the remaining wild type allele. This “two hits” model gives cells the survival advantage needed for tumor development.

The gross pathology of glucagonoma may show:^[7][8][9]

• Large tumors at diagnosis with a mean diameter of 5 cm. About 50 to 82% have evidence of metastatic spread at presentation.

• Nearly all glucagonomas are located in the pancreas, 50–80% occur in the pancreatic tail, 32.2% in the body and 21.9% in the head.
• In few patients, location can be extrapancreatic, such as in kidney, duodenum, lung, accessory pancreatic tissue.

• Metastasis usually occurs to the liver. Other sites are lymph nodes, bone, lung, and adrenals.

• Tumors smaller than 2 cm in diameter are associated with a very low chance of malignancy.

The microscopic pathology of glucagonoma tumors in pancreas usually show intense staining for glucagon.^[10][11]

• Many glucagonomas are pleomorphic with cells containing granules that stain for other peptides, most frequently pancreatic polypeptide.
• Immunoperoxidase staining can detect glucagon within the tumor cells and glucagon mRNA also may be detected.
• Electron microscopy shows secretory granules indicating the origin of glucagonoma from alpha cells.
• Benign tumors are usually fully granulated and malignant cells have fewer granules.
• Skin biopsy may depict epidermal necrosis.

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  Histology of confluent epidermal necrosis (high mag),Source:By Nephron – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16874054^[12]
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  Histology of confluent epidermal necrosis (very high mag)Source:By Nephron – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16874054^[12]
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  Histology of confluent epidermal necrosis (intermed mag)Source:By Nephron – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16874054^[12]

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