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.

Radiotherapy

Peptide Receptor Radionuclide Therapy (PRRT) or Radioisotope Therapy
  • Can be considered in both functional & nonfunctional NETs with a positive somatostatin receptor scintigraphy regardless of site of primary tumor
  • Radiolabeled cytotoxic agents are being investigated to target the overexpression of somatostatin receptors of the malignant pancreatic NETs
  • Lutetium Lu 177-dotatate is a radiolabeled somatostatin analog used as PRRT
    • Approved for the treatment of somatostatin receptor-positive gastroenteropancreatic NETs, including foregut,midgut & hindgut
  • Tumor-targeted treatment w/ radioactive octreotide derivatives 111In-D-Phe(1)-Tyr(3)-octreotide (111In-DOTA-octreotide) or 90Y-DOTA-octreotide & 177Lu-DOTA-octreotate & w/ 131I-MIBG are associated w/ varied response rates & clinical benefit
    • Patients w/ malignant NETS treated w/ [177Lu-DOTA-Tyr3]octreotide found a complete response in 2% of patients, partial response in 32% of patients, & stabilization in 34% of patients
    • Radiolabeled somatostatin analogs may also be considered for advanced pancreatic NETs
Radiation Therapy
  • External radiation therapy has limited value in NETs
    • Palliative option in patients w/ local disease when surgery is not feasible
    • Reserved for cases of known residual disease in which complete surgical resection is not possible
    • Often results in scarring & fibrosis which may interfere w/ tumor evaluation & make future surgical interventions difficult & potentially dangerous
    • Causes loss of somatostatin receptors on tumor cell surfaces which decreases the effectiveness of somatostatin analogs
  • Radiotherapy is only recommended for bone & brain metastases
    • Used to treat some bone lesions from malignant pheochromocytoma or paraganglioma, especially those that are rapidly growing
    • Effective in the treatment of pain from bone metastasis
    • Prophylactic cranial irradiation is considered in patients w/ small-cell lung cancer w/ successfully treated limited-stage disease & in patients w/ poorly differentiated neuroendocrine carcinomas of the head neck or unknown primary site
  • Recommended for thymic carcinoid tumors after surgery
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