ENSBORO, North Carolina (CNN) — Stomach cancer is rare in the United States, but that's not how it used to be. The American Cancer Society estimates about 21,320 cases of stomach cancer will be diagnosed in 2012 and about 10,540 people will die from the disease in the U. S. this year.

"Interestingly, it was a leading cause of cancer death in U.S. 100 years ago," says Otis Brawley, chief medical and scientific officer of the ACS and CNN's conditions expert. "Declines are due to refrigeration and less reliance on salted and cured foods."

Unfortunately, the same isn't true for the rest of the world. Stomach cancer is among the top 5 diseases that cause the majority of cancer deaths worldwide, according to the World Health Organization. It is most common in Eastern Asia, including Korea, Japan and China.

Mass screening is an important tool for the early detection of many cancers. "In countries such as Japan, where stomach cancer is very common, mass screening of the population has helped find many cases at an early, curable stage," the ACS website states.

A new study published this week in the scientific journal Cancer analyzed data from more than 2,000 patients who had been diagnosed with stomach cancer. Researchers divided the participants into seven groups based on time between their last clean endoscopy test and the endoscopy that detected their cancer.

The study authors concluded that the optimal time between stomach cancer screenings (in countries with a high prevalence) is three years.

"Gastric cancers are likely to become more advanced before detection with screening intervals that are longer than three years, but screening more frequently than every three years does not appear to be more beneficial," said Dr. Il Ju Choi in a press release. "The exception is if you have a family member with gastric cancer. In that case, you may need to undergo upper endoscopy screening more frequently."

Stomach cancers tend to develop slowly, which is why screening more frequently is unnecessary. Currently screening every two years is recommended in Korea for people over the age of 40, according to the study authors.

In the United States, controversy has surrounded screenings for some cancers in recent years, particularly when it comes to breast and prostate cancers. Scientific reviews of the benefits and risks brought about by routine prostate cancer screenings and breast cancer screenings have led to differing opinions by various medical groups about how often screenings are necessary, if at all.

The ACS does not recommend routine stomach cancer screening for people in the U.S. due to its low prevalence. Although a few patients with a history of H. Pylori infection (a bacteria that may cause stomach cancer) could benefit from screening, the gastrointestinal community has not come to a consensus, Brawley says.

The symptoms of stomach cancer include poor appetite, weight loss (without dieting), abdominal pain or swelling, heartburn, indigestion, or ulcer-type symptoms, nausea and vomiting. If you are experiencing any of these symptoms, please contact your doctor.

The-CNN-Wire/Atlanta
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