neuroendocrine%20tumors
NEUROENDOCRINE TUMORS
Neuroendocrine tumors are rare, small, slow-growing epithelial neoplasms with predominant neuroendocrine differentiation found in most organs of the body.
They arise from cells throughout the diffuse endocrine system.
Carcinoid tumors and pancreatic neuroendocrine tumors are the most common.
Carcinoid tumors arise from the lungs & bronchi, stomach, small intestine, appendix, rectum or thymus.
Majority of the neuroendocrine tumors are sporadic but some tumors are caused by inherited genetic syndromes such as multiple endocrine neoplasia, Von-Hippel Lindau disease, tuberous sclerosis complex and neurofibromatosis.
They have the ability to store and secrete various peptides and neuroamines.

Introduction

  • Majority of the neuroendocrine tumors (NETs) are sporadic but some tumors are caused by inherited genetic syndrome such as multiple endocrine neoplasia, Von-Hippel Lindau disease, tuberous sclerosis complex, & neurofibromatosis
  • They have the ability to store & secrete various peptides & neuroamines
    • Some of these substances can cause specific clinical syndromes while other substances may produce elevated plasma or urine levels that are not associated with a specific symptom complex or syndrome

Definition

  • Rare, small, slow-growing epithelial neoplasms with predominant neuroendocrine differentiation found in most organs of the body

Pathophysiology

  • Arise from cells throughout the diffuse endocrine system
  • Carcinoid tumors & pancreatic neuroendocrine tumors (NETs) are the most common
  • Carcinoid tumors arise from the lungs & bronchi, stomach, small intestine, appendix, rectum or thymus
  • Pancreatic NETs arise from the pancreas
  • Most common subtypes are:
    • Insulinomas that produce insulin
    • Gastrinomas which produce gastrin, a hormone that helps digest food
    • Glucagonomas that produce glucagon, a hormone that helps to raise blood sugar levels
    • VIPomas produce vasoactive intestinal peptide (VIP) that helps digestion & a number of other body processes
    • Somatostatinomas produce somatostatin that helps with digestion
  • Others less common NETs arise in the parathyroid glands, adrenal glands, pituitary gland, & calcitonin-producing cells of the thyroid gland

Signs and Symptoms

  • Flushing
    • Usually the dry type
    • Secondary to prostaglandins, kinins, & serotonin
    • Characteristic depends on the location of the tumor
  • Diarrhea
    • Commonly the secretory type
    • Produces large-volume stools
    • Persists with fasting
    • Relieved by proton pump inhibitor
  • Abdominal pain
    • Usually severe, persistent, & disturbs sleep
  • Dyspepsia
  • Ulcer
    • Relieved by proton pump inhibitor use that is very suggestive of gastrinoma diagnosis
  • Steatorrhea
  • Bronchoconstriction
    • Wheezing due to bronchospasm is seen in 1/3 of patients with carcinoid syndrome that is usually caused by substance P, histamine, or serotonin
  • Hypoglycemia
    • Seen in patients with insulinoma as part of Whipple triad (hypoglycemic symptoms <40 mg/dL, & relief of symptoms with glucose)
  • Hyperglycemia
  • Dementia
  • Dermatoses (eg urticaria, pellagra, cafe au lait)
  • Obstructive symptoms (eg nausea, vomiting, cholestasis)
  • Weight loss
Types of NETs based on Clinical Manifestation
Functional NETs
  • Symptoms are due to excess hormone production
  • Most common functionally active NETs include carcinoids, insulinomas, gastrinomas, VIPoma & glucagonomas
  • Most common manifestation is carcinoid syndrome caused by elevated levels of serotonin & is associated with carcinoid tumors from the small intestine or appendix
    • Symptoms of carcinoid syndrome:
      • Vasomotor symptoms (eg facial flushing, telangiectasia, chronic facial cyanosis, rhinitis)
      • Increased intestinal motility (eg diarrhea, borborygmi, abdominal pain)
      • Heart failure (eg endocardial fibrosis, pulmonary stenosis, tricuspid insufficiency)
      • Bronchoconstriction (eg asthma)
    • The presence of pancreatic mass without hormonal symptoms in a patient who has increased serum pancreatic polypeptide or chromogranin A (CgA) level is suggestive of non-functional NETs
Nonfunctional NETs
  • Most nonfunctional tumors are asymptomatic & not associated with clinical hormonal syndrome
  • Symptoms such as abdominal discomfort, diarrhea, bowel obstruction, weight loss, & jaundice are due to local growth & metastasis
  • They may not be diagnosed until they have progressed to advanced disease because they are slow-growing tumors
  • They are often found incidentally during imaging studies or surgery & their neuroendocrine origin may be noted only after histologic examination
  • They are still biologically active even though they do not secrete peptides which cause a clinical syndrome
    • The peptides that they secrete are used for their diagnosis (eg chromogranins, especially CgA, & pancreatic polypeptide)
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