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Tumours of the
Stomach |
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The most important tumour of the stomach is
adenocarcinoma
Gastric adenocarcinoma is more common in men than in women, and is seen in
patients after the age of 30, the incidence rising greatly after the age of 50
years.
There is marked geographic variation in the incidence of gastric cancer;
compared to Western Europe and North America, it is seen more frequently in the
Far East and certain parts of South America and Scandinavia. Because of the
great variation in geographical distribution, dietary aetiological factors have
been sought, but none are firmly proven. Frequent ingestion of smoked and salted
preserved foods has been implicated, particularly in the generation of
nitrosamines.
There is an association with blood group A.
Conditions predisposing to development of gastric carcinoma are chronic atrophic
gastritis and gastric adenomatous polyps. At-risk groups include patients with
chronic gastritis and intestinal metaplasia, post-gastrectomy patients with
persisting gastric inflammation, and patients in gastric cancer families (rare).
The pathogenesis of gastric carcinoma in the fundus and antrum is believed to
follow a sequence from normal mucosa, through chronic gastritis, intestinal
metaplasia, dysplasia and intramucosal carcinoma, to invasive carcinoma.
Carcinomas in the cardia are infrequently associated with chronic gastritis and
may have another pathogenesis.
Molecular pathology of gastric cancer
Gastric adenocarcinoma has three main growth patterns
Gastric adenocarcinoma may grow in a polypoid, ulcerating or diffuse
infiltrative pattern.
The diffuse infiltrative pattern tends to present very late. The symptoms are
usually those of non-specific loss of appetite, and food intolerance due to both
the small capacity of the stomach and its inability to distend under a food
load. Because surface ulceration is not a prominent feature, haematemesis is not
common until the late stage. Metastatic spread to lymph nodes and the liver is
usually present at the time of clinical presentation and, of the three types,
this pattern of growth has the worst prognosis.
The most common type is the ulcerative carcinoma. Characteristically, the ulcer
has a raised edge, a necrotic shaggy base, and the radiating folds seen in
benign peptic ulcers are absent.
The term early gastric cancer has been used to describe tumours that are
confined to the mucosa and submucosa. As these lesions may have metastases, the
term 'early' can be misleading. Such tumours are generally of the polypoid type
and have a better prognosis than other forms.
Histologically, adenocarcinoma of the stomach is divided into two main types.
The intestinal pattern of tumour is composed of gland-like spaces, and the
diffuse infiltrative carcinoma of the stomach is composed of sheets of
anaplastic cells, many of which have a single vacuole of mucin, displacing the
nucleus to one side (signet-ring cell).
Spread of gastric carcinoma is by four main routes
Adenocarcinoma of the stomach spreads by local, lymphatic, haematogenous and
transcoelomic routes.
• Direct invasion through the wall of the stomach leads to involvement of
adjacent viscera.
• Lymphatic spread (the main route ) is to nodes on the greater and lesser
curves of the stomach, then to other nodal groups. Involvement of the left
supraclavicular nodal group is well recognized (Virchow's node, Troisier's
sign).
• Haematogenous spread to liver, lung and brain is common. Spread to the ovaries
leads to development of Krukenberg tumours .
• Transcoelomic spread through the peritoneum results in malignant ascites.
Prognosis of gastric adenocarcinoma is poor in most cases. The five-year
survival rate in gastric carcinoma is low and depends on the stage of the tumour.
Many tumours are locally advanced at diagnosis and have spread to nodes or
metastasized. Prognosis after surgery is 20% 10-year survival for advanced
gastric cancer but 90% 10-year survival for lesions confined to the mucosa and
submocosa, as with small polypoid tumours. |
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