Patients with multiple primary gastric cancers tend to develop second primaries in organs other than the stomach.

The multiple occurrence of a single cancer tends to result in the increased vulnerability of some other organs to another malignancy. In the present study, we examined a total of 1,606 patients with gastric cancer to ascertain whether the frequency of second primaries in organs other than the stomach is higher in patients with multiple gastric cancers than in those with a single gastric cancer. Primary cancers of other organs were present in 87 (5.9%) of 1,474 patients with single gastric cancer and in 16 (12.1%) of 132 patients with multiple gastric cancers. The difference was statistically significant. The most frequent site of the occurrence of a second primary was the colo-rectum, followed by the urogenital organs, uterus, breast, and lung in descending order of frequency. We therefore assume that the occurrence of multiple cancers in the stomach is not merely a chance phenomenon but is related to both genetic predisposition and environmental factors.