Catherine Ley and Julie Parsonnet
Gastric cancer is the second most frequent cancer worldwide, representing almost 10% of all new cancers and surpassed only by lung cancer (1). It is also the 14th most common cause of death and the second most common cause of cancer death (2). Since the beginning of the century, however, gastric cancer incidence has been declining at a rate of 20-50% per decade (3). In the United States, for example, it has gone from, in 1940, the leading cause of cancer death to, in 1998, the ninth and tenth leading cause of cancer death in men and women, respectively (Fig. 1). Today, the incidence of gastric cancer in the United States is on the order of eight per 100,000 persons, although rates are higher among men than women and vary substantially across various racial and ethnic groups (4).
Gastric adenocarcinoma includes cancers of the noncardia, the cardia, and the gas-troesophageal junction. Noncardia cancers, which are the most common, are defined as cancers of the antrum, corpus, and fundus (5-7); it is the incidence of these cancers that is declining around the world. Noncardia tumors have been directly associated with H. pylori and are the focus of the current chapter. Cancers of the cardia and gas-troesophageal junction, which are less common, appear to be on the increase, currently constituting up to 50% of stomach cancers in some areas (7).
Several histologic systems exist to classify gastric cancers. The Lauren system classifies gastric adenocarcinoma into two types: intestinal and diffuse (8). The intestinal type, which predominates around the world, is decreasing rapidly in frequency (9,10). It commonly arises in the gastric antrum and is characterized by cohesive cells that form discrete glands. Such intestinal tumors are preceded by a series of precancerous lesions, starting with chronic atrophic gastritis, progressing to intestinal metaplasia, dysplasia, and finally to cancer; this sequence occurs over several decades (9) (Fig. 2). Diffuse-type carcinomas are declining in incidence at a slower rate. They are more common in developed countries, generally involve the fundus and cardia, and are less differentiated, characterized by cells without gland formation and with occasional ring cells and mucin. Precursor conditions for diffuse type adenocarcinomas are not defined.
The prognosis of gastric adenocarcinoma relates to the extent of the disease. In Japan, where gastric cancer is extremely common, persons undergoing routine screen-
From: Infectious Causes of Cancer: Targets for Intervention Edited by: J. J. Goedert © Humana Press Inc., Totowa, NJ
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