Dr.vahedian ardakani
Medical oncologist
91/11/5
Neuroendocrine tumors (NETs) are derived from
the diffuse neuroendocrine system, which is made
up of peptide- and amine-producing cells with
different hormonal profiles depending on their
site of origin.
Pathologists cannot differentiate benign from
malignant carcinoid tumors based on histologic
analysis, nor can they histologically differentiate
pancreatic endocrine tumors from carcinoid
tumors.
Malignancy can only be determined by local
invasion or distant metastases.
Carcinoid tumors synthesize bioactive
amines and peptides, including
neuron-specific enolase (NSE),5-hydroxytryptamine serotonin
(5-HT), synaptophysin, and chromogranin A and C, and
other peptides like insulin, growth hormone, neurotensin,
adrenocorticotropic hormone (ACTH),
j3\melanocytestimulating
hormone, gastrin, pancreatic polypeptide, calcitonin,
substance P, other various tachykinins (neuropeptide- K),
growth hormone-releasing hormone, bornbcsin, and various
growth factors such as transforming growth factor-S,
plateletderived growth factor, and fibroblast growth factorj3
Neuroendocrine tumors (NETs) arising at different sites
within the body are classified according to their
histologic features.
All commonly used classification systems reflect a basic
separation between more indolent, well differentiated
tumors (traditionally referred to as carcinoids, islet cell,
or pancreatic NETs), and far more aggressive poorly
differentiated types that behave clinically more like
small cell neuroendocrine tumors.
Neuroendocrine tumors of the lung encompass a
spectrum of tumors, including
low-grade typical carcinoid,
Intermediategrade atypical carcinoid,
high-grade large cell neuroendocrine
carcinoma (LCNEC),
and SCLC
Carcinoid tumors are rare, but are »
the most common gastrointestinal
neuroendocrine tumor
Carcinoids arise from enterochromaffin
cells of the gastrointestinal tract. They have
traditionally been classified based upon
their origin from the embryonic divisions of
the alimentary tract; the foregut, midgut, or
hindgut. In addition, they are classified
based upon histologic characteristics as
"typical" or "atypical" (anaplastic).
the majority of carcinoids were located in the »
gastrointestinal tract (55 percent) and
bronchopulmonary system (30 percent)
Within the gastrointestinal tract, most »
carcinoids arose in the small intestine (45
percent, most commonly in the ileum), followed
by rectum (20 percent), appendix (16 percent),
colon (11 percent), and stomach (7 percent).
The distinction between benign and malignant
carcinoid is based upon the presence or
absence of metastases rather than histology
alone.
The metastatic potential of carcinoids
correlates best with the size and the site of the
primary tumor.
.Clinical symptoms may be general, or they
may correlate with the location of the tumor
and be organ related.
Symptoms of the carcinoid syndrome (eg, flushing
and diarrhea) are infrequent, occurring in
approximately 5 to 7 percent of patients. The
frequency of carcinoid syndrome varies with
tumor site and presence of metastases. Among
patients with intestinal carcinoid tumors, the
carcinoid syndrome does not occur in the absence
of liver metastases.
Gastric carcinoids may present with peptic ulcer
disease, abdominal pain, or bleeding. Gastric
tumors are subclassified into types that have
different presentations and malignant potential
Small intestinal carcinoids may present with
abdominal pain and/or intermittent obstruction.
Appendiceal carcinoids are the most common
neoplasm found in the appendix; they are most
often discovered incidentally
Transverse, descending colon, and rectum tumors
may present with changes in bowel habit,
obstruction, or bleeding.
.
Ovarian carcinoids can produce the carcinoid »
syndrome without hepatic metastases due to
their direct drainage into the systemic
circulation
The clinical value of SRS in the initial evaluation
or routine follow up of patients with advanced
NET has been called into question. Baseline SRS
may still be useful, however, as the uptake of
radiolabeled octreotide is predictive of a clinical
response to therapy with somatostatin analogs
The predominant site of metastatic
spread is the liver. Patients in whom
metastatic disease is suspected should
be evaluated with a triple-phase
contrast-enhanced helical CT or an MRI
scan to rule out liver metastases. Some
physicians prefer MRI because of its
greater sensitivity for liver metastases.
Changes in biochemical markers are associated
with disease progression and/or response to
treatment. Elevated urinary levels of 5hydroxyindoleacetic acid (5-HIAA) are highly
specific for serotonin-producing carcinoid tumors
(ie, those arising in the midgut), although they are
not sensitive.
For non-serotonin producing carcinoids and
pancreatic neuroendocrine tumors, serum
chromogranin A (CGA) is a more sensitive than 5HIAA, though serum levels of CGA can also be
elevated in non-neuroendocrine related
conditions.
Pancreatic neuroendocrine tumors (pNETs) are low- to
intermediate-grade neoplasms that are thought to arise
from the pancreatic islets.
Also known as pancreatic endocrine tumors,
islet cell carcinoma, or pancreatic carcinoid, pNETs
account for a minority of pancreatic neoplasms and can
be either functional or nonfunctional.