Multiple primary cancers subsequent to gastric cancer in Hokkaido Cancer Center.

The occurrence of multiple primary malignant neoplasms in 607 patients with gastric cancer (404 males and 203 females) and 166 patients with peptic ulcer (136 males and 30 females) was examined by follow-up study. All patients were gastrectomized and had follow-up data from 2 to 13 years. The observed number of multiple primary cancer cases was compared with the expected number calculated from person-years of cases multiplied by the sex/age-specific incidence in Hokkaido. The frequency of a second primary cancer, including synchronous cancer, in gastric cancer patients was higher than that in peptic ulcer patients, and this tendency was also confirmed by the standardized incidence in the UICC standardized population. However, this difference disappeared after subtraction of synchronous cases. Therefore, the chance of a second cancer in gastric cancer patients seemed to be the same as that in the general population at least one year after the operation.