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Introduction
Gastric or stomach cancer is
one of the most common cancers worldwide with the highest
incidence in areas such as Japan, Korea, South America,
and Eastern Europe. The incidence
is much lower in the United States with about 22,000 new
cases per year. The overall incidence of gastric
cancer in the United States is decreasing, but cancers
of the upper stomach and stomach-esophagus (gastroesophageal)
junction are increasing. These tumors typically occur
in people in their 60s and 70s, but can also occur in younger
and older individuals.
The vast majority of gastric cancers are classified as adenocarcinomas,
which are tumors arising from the inner mucosal lining
of the stomach. These tumors grow from this inner
lining and can spread to the deeper layers of the stomach. Eventually,
tumors can penetrate the stomach wall and invade adjacent
organs or spread along the peritoneum (the inner lining
of the abdomen). In addition, gastric cancers can
spread through lymphatic vessels to regional lymph nodes
and though the bloodstream to the liver and lung. The
goal of surgical resection of gastric cancer is to remove
the involved stomach and regional lymph nodes before the
tumor can spread to other sites.
Gastric cancers not classified as adenocarcinomas comprise
only 5-10% of all gastric cancers. These cancers
include lymphomas, gastrointestinal stromal tumors (GIST),
and neuroendocrine tumors (carcinoids). The remainder
of the information presented will be specific for gastric
adenocarcinomas except as noted below.
Diagnosis & Workup
Clinicians at Massachusetts General Hospital
have developed a standardized algorithm for the diagnosis and
workup of gastric cancers.
Medical history and physical examination
The medical history
is required to determine all symptoms, possible risk factors,
and other medical problems. Physical
examination is essential to rule out distant spread of
disease.
Diagnostic Imaging
The initial diagnostic test
to identify a gastric cancer is an endoscopic examination of
the stomach (upper endoscopy). Upper
endoscopy can accurately identify abnormalities in the
lining of the stomach, where gastric adenocarcinomas originate. An
even more sensitive study is an endoscopic ultrasound,
which combines an endoscopy with an ultrasound probe. This
study can identify how deep the tumor has penetrated into
the gastric wall and identify disease in regional lymph
nodes.
The definitive diagnosis of gastric cancer requires a biopsy,
which is performed at the time of upper endoscopy. Once
the diagnosis is established, a workup is performed to
determine if the cancer is localized or has spread to other
sites. The most common sites of spread of gastric
cancer are to regional lymph nodes, peritoneum, liver,
and lung. Abdominal CT scans can often identify gastric
wall thickening but overall is a relatively insensitive
method of identifying gastric tumors. However, chest,
abdomen, and pelvic CT scans are very useful for ruling
out the spread of disease beyond the stomach.
Laparoscopy
Gastric cancers can shed small deposits of tumor
cells throughout the peritoneum, and this mode of spread is
difficult to detect by any radiologic study. A procedure
called laparoscopy is very sensitive in detecting peritoneal
spread of tumor, and is often performed prior to surgical
resection of gastric cancers. In this procedure,
two or three tiny incisions are made in the abdominal wall,
and a telescope and other small instruments are inserted
into the abdomen.
Treatment
Gastric cancer can be treated with combinations of surgery, radiation therapy,
and chemotherapy depending on the location and extent of disease.
Surgery
Surgery remains the primary treatment modality
for gastric cancer. Ideally, tumors should be removed with
a margin of normal tissue of about 3-5 centimeters
(about two inches). However, gastric cancers
often arise in difficult anatomic locations and may
require extensive surgical expertise to remove in their
entirety with the best possible margin. Gastric
cancers arising in the distal or lower portion of the
stomach often can be removed without removal of the
entire stomach (subtotal gastrectomy). Cancers
arising in the proximal or upper stomach usually require
removal of the entire stomach (total gastrectomy) and
connection of the small bowel to the esophagus.
There is uniform agreement among gastric cancer
specialists that the regional lymph nodes around
the stomach should routinely be removed during
resection of a gastric cancer and that at least
15 lymph nodes should be analyzed for adequate
staging. This lymph node dissection
is called a D1 lymphadenectomy. However, a recent
large multi-center trial involving hospitals throughout
the United States showed that the majority of patients
(> 50%) did not receive even this minimum
lymph node dissection.
There
is ongoing controversy over whether a lymph node
resection beyond a D1 lymphadenectomy is beneficial. Experienced
gastric surgery centers, especially in Japan and Korea,
have argued that a more extensive lymph node dissection
that incorporates the next echelon of lymph nodes (D2
lymphadenectomy) improves staging and outcome in gastric
cancer patients. The
two largest Western trials examining this issue did
not find a benefit to D2 lymphadenectomy. However,
these studies had several flaws including a technique
of D2 lymphadenectomy that unnecessarily included resection
of the spleen and portion of the pancreas, leading
to increased complications and mortality from surgery. A
recently published randomized trial published in Lancet
Oncology of 221 patients from Taiwan showed that overall
survival was significantly higher in patients that
underwent a more extensive lymph node resection compared
to a D1 lymph node resection.
Examples:
Subtotal Gastrectomy & D2
Lymphadenectomy |
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Total Gastrectomy & D2
Lymphadenectomy |
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This image demonstrates the operative
field after removal of the distal
stomach along with an extended
D2 lymphadenectomy. For
a D1 lymphadenectomy, nodes along the left
gastric artery, splenic artery, common
hepatic artery, proper hepatic artery,
and gastroduodenal artery are not resected.
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This image demonstrates the operative
field after removal of the entire stomach
along with an extended D2 lymphadenectomy. For
a D1 lymphadenectomy, node along the
left gastric artery, splenic artery,
splenic hilum, common hepatic artery,
proper hepatic artery, and gastroduodenal
artery are not resected. |
Several studies have demonstrated that the outcome
of patients following surgery for gastric cancer
is related to surgical experience and hospital
volume. The surgical oncologists at
the Cancer Center have all received specialty
training in gastric cancer surgery and believe
that gastric resection along with D2 lymphadenectomy
can be performed safely and may improve survival
in a subset of patients with gastric cancer. In
addition, surgeons at Massachusetts General Hospital
perform more surgeries for gastric cancer than
any other hospital in New England.
Chemotherapy and Radiation Therapy
Gastric
cancers have the ability to spread to distant sites,
most frequently to the peritoneum, liver, and lung. Chemotherapy may be beneficial
to patients even if no sites of distant disease
are identified in order to kill microscopic foci
of tumor cells. If macroscopic distant disease
is identified, chemotherapy may be beneficial in
decreasing the growth and spread of disease.
Chemotherapy is usually given in combination with
radiation therapy after surgical resection of the
gastric cancer. A recent trial published
in the New England Journal of Medicine showed that
patients receiving chemotherapy and radiation therapy
after surgical resection of gastric cancer had
improved survival compared to those treated with
surgery alone. However, this trial enrolled
patients after surgical procedures with no quality
control. Thus over half of patients received
inadequate lymph node resections. There was
no survival advantage in the subgroup of patients
who received a D2 lymphadenectomy, although the
number of patients in this subgroup was likely
inadequate to form a definitive conclusion.
A recent trial (MAGIC trial) presented at the American
Society of Clinical Oncology meeting in 2005 showed
that patients who received a combination of epirubicin,
cisplatin, and 5-fluorouracil (ECF) before and
after surgery had improved survival compared to
patients who underwent surgery alone. Currently,
many patients at Massachusetts General Hospital
are either receiving the ECF regimen outlined by
the MAGIC trial or are entering a study randomizing
patients after surgery to standard 5-fluorouracil
and radiation therapy or ECF combined with
5-fluorouracil and radiation therapy.
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