The risk of gastrointestinal and other primary malignant diseases following gastric cancer.

The risk of developing a second primary cancer was studied among 34,506 gastric cancer patients identified through the Swedish Cancer Registry. A second cancer was reported in 962 patients compared to an expected number of 826 (relative risk = 1.16, 95% confidence limits = 1.09-1.24). The slightly but significantly elevated risk was largely confined to the first year after the gastric cancer diagnosis, and to patients under 70 years old at the time of diagnosis. The risk was significantly increased for cancer in the small intestine, colon, rectum, kidney, breast and prostate. A closer look at the data, however, revealed that a substantial proportion of the second cancers were diagnosed within one month after the gastric cancer diagnosis, or at autopsy. We recalculated the relative risk estimates under the assumption that only 75% of the cancers incidentally detected in connection with diagnosis/treatment of the gastric cancer would have become clinically manifest during the relatively short observation time. and that 20% of the cancers revealed at autopsy in the gastric cancer patients would have been detected if the death and autopsy rates in this group had been equal to those in the general population (matched for age and gender). Under those assumptions the risk of having a second primary cancer among gastric cancer patients was close to what would be expected. The increased risk reported in some previous studies could be the result of closer patient surveillance.