Carcinoid Syndrome (cont.)
Where do carcinoid tumors occur?
Carcinoid tumors can be found wherever there are enterochromaffin cells,
essentially, throughout the body. The majority (65%) of carcinoid tumors are
found in the gastrointestinal tract. The origin of gastrointestinal carcinoid
tumors is most commonly the small intestine, appendix, and rectum. Less common
origins are the stomach and colon; and the least common origins are the
pancreas, gallbladder, and liver (though carcinoid tumors in the liver
usually are metastasis from elsewhere).
Approximately 25% of carcinoid tumors are found in the bronchial airways and
the lung. The remaining 10% can be found almost anywhere. In some cases, doctors
cannot locate the site of origin of the carcinoid tumors, though they know by the
symptoms of the carcinoid syndrome that they are present.
Small intestinal carcinoid tumors
In general, small intestinal tumors (whether benign or cancerous) are rare,
much more rare than colon or
stomach cancers. Nevertheless, carcinoid tumors comprise one third of all small
intestinal tumors, and are most commonly found in the ileum (the lower part
of the small intestine close to the colon). Small intestinal carcinoid tumors
typically produce no symptoms or produce only vague abdominal pain. Therefore,
it is difficult to detect carcinoid tumors of the small intestine early, while
they still can be completely removed and the patient cured. The few small
carcinoid tumors that are found early usually are found incidentally when x-rays
or procedures are performed for other purposes. Typically, small intestinal
carcinoid tumors are diagnosed late, often years after the onset of symptoms and
usually after local and distant metastases already are present.
Approximately 10% of small intestinal carcinoids cause the carcinoid
syndrome. Presence of the carcinoid syndrome usually means that the tumor is
malignant and has spread to the liver.
Small intestinal carcinoid tumors often obstruct the
small intestine when they reach a large size. Symptoms of small bowel
obstruction include crampy abdominal pain, nausea and vomiting, and sometimes diarrhea. Obstruction can be
caused by two different mechanisms. The first mechanism is by enlargement and
growth of the tumor into the lumen (channel) within the small intestine. The
second mechanism is by kinking of the small intestine due to fibrosing
mesenteritis, a condition caused by the tumor in which extensive scarring occurs
in the tissue surrounding the small intestine. Fibrosing mesenteritis sometimes
obstructs the arteries supplying blood to the intestines, resulting in death of
a portion of the intestine (gangrene). The
gangrenous intestine can rupture and
be life-threatening.
Appendiceal carcinoid tumors
While tumors of the appendix are rare, carcinoid tumors are the most common
tumor of the appendix, comprising approximately half of all appendiceal tumors.
In fact, carcinoid tumors are found in 0.3% of resected (removed) appendices, but most of
them are smaller than 1 cm and do not cause symptoms. They are found mostly in
appendices removed for unrelated reasons. Most authorities believe that
appendectomy is
adequate treatment for these small appendiceal carcinoid tumors. The chances
that a tumor would recur after appendectomy are very low.
Appendiceal carcinoid tumors larger than 2 cm at the time of diagnosis have
approximately a 30% chance of being malignant and having local metastases. Thus,
larger appendiceal carcinoid tumors need more extensive surgery such as removal
of the right colon rather than simple appendectomy. Fortunately, large
appendiceal carcinoid tumors are rare. Carcinoid tumors limited to the appendix,
even metastatic to local tissues, usually do no cause the carcinoid syndrome.
Rectal carcinoid tumors
Rectal carcinoid tumors are often discovered
incidentally at the time of flexible sigmoidoscopy or colonoscopy. Carcinoid
syndrome is rare with rectal carcinoid tumors. The probability of having metastases (malignant carcinoid)
correlates with the size of the tumor; those larger than 2 cm have a 60-80%
chance of having metastases, and those smaller than 1 cm have less than a 2 %
chance of having metastases. Therefore, small rectal carcinoid tumors usually
can be successfully removed by simple excision, but the larger tumors (larger
than 2 cm) need more extensive surgery that may involve removal of part of the
rectum.
Gastric (stomach) carcinoid tumors
There are three types of gastric (stomach) carcinoid tumors; types I, II, and
III.
Type I gastric carcinoid tumors, which account for 75% of gastric carcinoids, are typically smaller
than 1 cm and usually are benign. There can be multiple tumors scattered
throughout the body of the stomach. They typically develop in patients with
pernicious anemia or chronic atrophic gastritis, conditions in which the stomach
stops producing acid. The lack of acid causes the cells in the stomach that
produce the hormone gastrin to secrete large amounts of gastrin into the blood.
(Gastrin is a hormone normally produced by the body to stimulate stomach acid.
Acid in the stomach shuts off the production of gastrin. In pernicious anemia or chronic atrophic gastritis, the lack of acid results in the
production of increasing amounts of gastrin.) Gastrin, in addition to
stimulating acid, also stimulates the growth of enterochromaffin cells in the
stomach into benign carcinoid tumors. Treatment of type I carcinoid tumors
include medications such as the somatostatin-type drugs which shut off
production of gastrin or surgical removal of the gastrin producing part of the
stomach.
Type II gastric carcinoid tumors are extremely rare and are very slow growing with a low probability
of becoming malignant. They occur in patients with a rare genetic disorder
called MEN (multiple endocrine neoplasia) type I. These
patients have tumors in other endocrine glands such as the pituitary gland,
parathyroid gland, and the pancreas.
Type III gastric carcinoid tumors tend to be larger than 3 cm and tend to be sporadic (occurring one or
two at a time) in otherwise normal stomach (without the presence of pernicious
anemia or chronic atrophic gastritis). Type III tumors usually are malignant and
tend to invade deep into the stomach wall and metastasize. Type III tumors can cause local symptoms of abdominal pain and
bleeding, as well as symptoms due to carcinoid syndrome. Type III gastric
carcinoids usually require surgical removal of the stomach as well as the
surrounding lymph nodes.
Colonic carcinoid tumors
Colonic carcinoid tumors typically occur in the right
colon (ascending colon and right half of the transverse colon). Like small bowel carcinoid tumors,
colonic carcinoid tumors are often discovered late. Thus, the average size of
the tumors at the time of diagnosis is 5 cm, and metastases are present in two
thirds of patients. Carcinoid syndrome is rare with colonic carcinoid tumors.
Next: How are carcinoid tumors and carcinoid syndrome diagnosed? »
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