Gastric Cancer: The Basics

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Gastric Cancer: The Basics
Ryan P. Smith, MD and Eric Shinohara, MD, MSCI
Affiliation: Abramson Cancer Center of the University of Pennsylvania
Last Modified: February 23, 2008
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What is the stomach?
Gastric cancer is cancer of the stomach. The stomach is the organ that holds and stores food. It is located just underneath (deep to) the lower portion of the rib cage on the left side. It is connected to the mouth and throat by the esophagus. The stomach contains acid and is quite muscular. Due to the motion of the stomach and the acid, quite a bit of digestion takes place in the stomach. The partially digested food is then emptied into the small intestine so that absorption of the nutrients from food can take place. Although the stomach obviously cannot be directly visualized, it can be seen via an endoscopy procedure using a fiber-optic camera (see below).

What is gastric cancer?
The definition of a tumor is a mass of quickly and abnormally growing cells. Tumors can be either benign or malignant. Benign tumors have uncontrolled cell growth, but without any invasion into normal tissues and without any spread. A malignant tumor is called cancer when these tumor cells gain the propensity to invade tissues and spread locally as well as to distant parts of the body. In this sense, gastric cancer occurs when cells in the lining of the stomach grow uncontrollably and form tumors that can invade normal tissues and spread to other parts of the body.

Cancers are described by the types of cells from which they arise. Over 90% of gastric cancers arise from the lining of the stomach. Since this lining has glands, the cancer that comes from it is called adenocarcinoma. Although there are other cancers that can arise in the stomach (lymphomas-from lymph tissue, leiomyosarcoma-from muscle tissue, squamous cell carcinoma-from lining without glands), the vast majority are adenocarcinomas. Hence, these are the most commonly studied.

Am I at risk for gastric cancer?
In the United States, there are about 22,000 gastric cancers annually, with about 11,00 deaths attributed to this disease each year Interestingly, its incidence has drastically decreased since 1930. Although it is presumed that this is due to some sort of dietary or environmental factor(s), the exact reason behind this decrease is not known. One theory is that the advent of refrigeration led to decreased use of nitrites, “smoking” of foods, and other such forms of food preservation. It also decreased food contamination. Gastric cancer is approximately twice as common in men and more common in Blacks than Caucasians. It is rare to see gastric cancer before the age of 40, and its incidence increases with age thereafter. There are two types of gastric cancer, the intestinal type and the diffuse type; the latter carries a worse prognosis.

Although gastric cancer has greatly decreased in the United States, on a worldwide scale its incidence is still high, and it is the second leading cause of cancer death worldwide, behind lung cancer. Its highest incidence is in East Asia (e.g.-Japan, China), presumably because of a diet consisting of heavily smoked, salted, and pickled foods. Interestingly, first generation immigrants from these countries have a decreased incidence of stomach cancer after moving to the United States, but it is still higher than the general American population. However, the incidence greatly declines in second and third generation Japanese and Chinese immigrants to the United States, pointing to the fact that there does not appear to be an inherently genetic component in Eastern Asians’ preponderance to gastric cancer, but rather an environmental component.

As mentioned above, diets heavily salted, smoked, or pickled are associated with an increased risk of disease, while diets rich in fruits, vegetables, and dietary fiber are associated with a decreased risk of cancer. The incidence of gastric cancers also increases with decreasing socioeconomic status, likely due to a number of social, occupational, and cultural factors. Tobacco use has also been associated with an increase in gastric cancers. There does not appear to be a link with alcohol consumption.

There does appear to be a genetic link in some cases of gastric cancer, and there are some genetic diseases such as hereditary nonpolyposis colorectal cancer, familial adenomatous polyposis, and Peutz Jeghers syndrome which all predispose to gastric cancer. It also appears that people with blood type A are at increased risk for gastric caner for an unknown reason.

Studies have also linked infection with Helicobacter pylori with gastric cancer. H. pylori is associated with gastric ulcers and chronic atrophic gastritis, which may explain the high incidence of gastric cancer in patients infected with H. pylori. However, the exact role of H. pylori in the development of gastric cancer remains unclear. It is theorized that H. pylori causes a gastritis or inflammation of the stomach, which can lead to a loss of secretory cells in the stomach, also known as strophic gastritis. It is believed that this process of atrophy can lead to gastric cancer. H. pylori has also been linked to lymphomas of the stomach.

Pernicious anemia, an autoimmune disease where the stomach does not produce stomach acid, has also been linked to gastric cancer. Drugs which cause a decrease in stomach acid production have not been linked to an increased risk of gastric cancer.

It should be noted that, although these risk factors are listed above, the majority of gastric cancers develop without any one obvious predisposing cause. In other words, there is no extremely strong cause effect relationship with any risk factor, in contrast, for example, to that between smoking and lung cancer.

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