Cancer of the lower stomach has decreased overall in American adults but has increased in whites age 25-39, a study finds. The work, led by researchers from the National Cancer Institute (NCI), part of the National Institutes of Health, is published in the May 5, 2010, issue of the Journal of the American Medical Association.

Cancers of the upper and lower parts of the stomach are thought to have different causes. Cancers of the upper stomach may be related to acid reflux, whereas a major cause of lower stomach cancers is infection with the bacterium Helicobacter pylori (H. pylori). Most stomach cancers are diagnosed in people 65 years of age or older. In the United States, stomach cancer is higher among African-Americans, Asian-Americans, and Hispanics.

"Overall stomach cancer incidence trends primarily reflect higher rates in older individuals," said study author William F. Anderson, M.D., Division of Cancer Epidemiology and Genetics, NCI. “But incidence rates that are specific to particular age groups can provide important clues about future cancer trends that may vary from group to group."

The research team analyzed data from NCI’s Surveillance, Epidemiology and End Results (SEER) program, which collects cancer incidence and survival data from population-based registries that cover 26 percent of the U.S. population. The NCI team identified 39,003 cases of noncardia gastric cancer diagnosed from 1977 through 2006. They then compared changes in incidence rates during this 30-year period in groups defined by age, race, and other factors.

The researchers found that the overall incidence rates (cases per 100,000 people) of noncardia gastric cancers declined over the 30-year study period for all races. Specifically, rates dropped from 5.9 to 4.0 among whites, from 13.7 to 9.5 among blacks, and from 17.8 to 11.7 among other racial groups. However, among whites, different age groups had markedly different incidence rate trends. Even though incidence rates fell from 20 to 13 among people age 60-84, and from 3 to 2 among those ages 40-59, they increased from 0.27 to 0.45 among those ages 25-39. In contrast, incidence rates of noncardia cancer declined for nearly all age groups among blacks and people of other races.

While noncardia gastric cancer risk is substantially greater for Hispanic than non-Hispanic whites, the SEER data did not distinguish ethnicity-specific rates until 1992. The investigators conducted an analysis for the time period 1992-2006 among non-Hispanic whites and observed similar age-specific trends as seen as during the entire study period 1977-2006 among whites overall.

Because infection of the stomach lining by H. pylori is a primary cause of noncardia gastric cancer, changes in infection patterns during the last 50 years might explain the difference in incidence trends between younger and older whites. The declines in noncardia gastric cancer seen in the older cohorts are consistent with observed declines in H. pylori infection, reflecting improved hygiene and less crowding during childhood, when the infections are typically acquired. The increase in younger cohorts may indicate a change in the age at infection or even a reversal of the long-term decline in the prevalence of the infection.

The scientists say it may also be possible that a new carcinogenic process is emerging, perhaps unmasked by eradication of H. pylori.

Apart from H. pylori infection, nutritional exposures, such as consuming salt and salt-preserved foods, have been implicated as risk factors for noncardia gastric cancer. Tobacco smoking is another risk factor for upper and lower stomach cancers.

"Fortunately, the overall burden of stomach cancer has been declining among all racial groups in the United States. However, increasing rates in 25-to-39 year old whites could mean there is an important new risk factor to be identified," said Charles S. Rabkin, M.D., senior author of the NCI study.

The team concludes that additional studies are needed to confirm the trends and investigate risk factors for stomach cancer in younger whites.