gastric cancer

gastric cancer

Epidemiology

The incidence of gastric cancer is high in countries such as Japan, China and those in South America. The incidence is low in North America, Australia, and Western Europe. In North America there has been a steady decline in both incidence and mortality since accurate records have been kept. At the present time in North America the mortality is 7 per 100,000 for men and 4 per 100,000 for women. Nevertheless, despite this fall, it is still a relatively commonly encountered type of malignancy and represents approximately 3 % of all cancer deaths. In British Columbia cancer of the stomach is mainly (but not exclusively) encountered in immigrants, particularly those from SE Asia and Eastern Europe. Population data from San Francisco suggests that the children of immigrants are much less likely to develop gastric cancer than their parents, and that the grandchildren of immigrants have the same incidence as the general population. In the United States gastric cancer is commoner among poor people (especially African Americans). In all population groups studied, it is commoner in men than women.

Gastric cancer occurs most commonly in the elderly. Nevertheless it is not confined to that age group and may affect individuals between the ages of 40 and 60. Carcinoma of the stomach occurring under the age of 40 is regarded as a rarity. Because most gastric cancers are aggressive neoplasms and because they tend to present late in the course of the disease when metastasis has already occurred and the prognosis is poor even when radical surgery has been performed.

Classification

A simple classification of gastric cancer is given in the accompanying figure.

Classification of Gastric Neoplasms

Benign

Adenoma

Benign stromal tumors

Malignant

Distal gastric adenocarcinoma

Diffuse carcinoma

Cardiac carcinoma

MALT lymphoma, small and large cell types

Sarcoma

Distal gastric cancer

This still accounts for approximately 55 % of all gastric cancers diagnosed in British Columbia. As the name suggests, it occurs predominantly in the distal portion of the stomach, especially antrum but also in the distal body. Grossly it consists usually of a well-circumscribed lesion that may be polypoid or ulcerated. Microscopically the tumor is an adinocarcinoma composed of poorly formed tubules. Because of its resemblance to colon cancer it is sometimes referred to as an intestinal type of cancer. Distal gastric cancer may present with non-specific generalized symptoms such as weight loss or iron deficiency anemia (due to bleeding). Occasionally, the mass effect may cause pyloric obstruction. Metastatic spread is in three directions: a) to regional lymph nodes and later to more distal lymph nodes such as those in the neck; b) via the blood stream to the liver and later to the lungs; c) trans coelomically resulting in ascites or metastases to the ovaries.

The term “early gastric cancer” refers to a neoplasm which has its growth confined to the gastric mucosa and submucosa. These neoplasms have a much better prognosis than advanced carcinomas (greater than 80% 5-year survival). Early cancers are commonly diagnosed in Japan where endoscopic surveillance programs exist, but are rare in Canada where late diagnosis is the rule.

A reduction in distal gastric cancer accounts almost entirely for the overall reduced incidence of gastric cancer in westernized countries. The reasons for this are discussed below.

Diffuse gastric cancer

This disease accounts for approximately 10 – 15% of cases of gastric cancer. It has a worldwide distribution and is less heavily concentrated in the older age groups. The name diffuse was given because this cancer spreads throughout the stomach in a single cell infiltrating pattern that often has no grossly or microscopically identifiable border. The tumor is often accompanied by a proliferative fibrosis of the surrounding tissues which results in shrinkage of the stomach to form a rigid “leatherbottle” appearance. An old fashioned name for this type of tumor is linitis plastica. This type of tumor often has no definite mucosal lesion and its presence can only be suspected endoscopically by the presence of either enlarged mucosal folds or flattened folds.

Microscopically the tumor grows as individual cells. These may contain globules giving rise to the appearance of “signet ring cells”. Diffuse tumors spread widely and have an extremely poor prognosis. Metastatic signet ring cell carcinoma to the ovary is termed “Krukenbergs tumor”.

Cardiac gastric cancer

Cardiac cancer now accounts for approximately 35 – 40% of gastric cancers diagnosed in British Columbia. The incidence of this tumor appears to be increasing. Unlike distal gastric cancer it is a disease associated with affluence, not poverty. The incidence is considerably higher (possibly up to 7 times) in men as it is in women. Grossly and microscopically this tumor resembles distal gastric cancer. However, it is located either at the gastroesophagial junction or very close to it. These tumors may present insidiously, but are often accompanied by dysphagia.

Gastric lymphoma

The vast majority of gastric lymphomas arise from MALT. Both low-grade and high-grade lymphomas are recognized and occur in approximately equal numbers. High-grade lymphomas clinically present like and grossly resemble carcinomas. The distinction may only be made on biopsy. They metastasize to regional lymph nodes and are treated by gastrectomy combined with chemo/radiotherapy. Low-grade gastric lymphomas are relatively indolent, but may evolve into high-grade lymphomas. At the present time it is considered that all gastric lymphomas arise as a result of lymphoid proliferation secondary to gastric infection by Helicobacter pylori.