Risk of gastric cancer in hereditary nonpolyposis colorectal cancer in Korea.

After endometrial cancer, gastric cancer is the second most common extracolonic cancer in cases of hereditary nonpolyposis colorectal cancer (HNPCC), where the relative risk in HNPCC familial members is known to be 4-fold. However, it is not yet clear whether HNPCC families from Korea, an endemic area for gastric cancer, have the same relative risk or whether the incidence of gastric cancer is high enough to justify familial screening. To clarify these questions, we investigated 1011 individuals from 66 Korean HNPCC families (28 families fulfilled the Amsterdam criteria and 38 did not). The overall and age-specific relative risk of gastric cancer in HNPCC families when compared with the background population was calculated. Twenty-five patients with gastric cancer were identified from among 22 HNPCC families. The calculated risk of gastric cancer in patients with HNPCC and their first-degree relatives was 2.1-fold greater than in the general population (95% confidence interval; range, 1.4-3.2). However, the relative risk of gastric cancer in the younger generations was much greater (11.3-fold in the 30s and 5.5-fold in the 40s). Additionally, the relative risk was greater in mutation carrier families than noncarrier families (3.2-fold versus 1.6-fold). This study demonstrates that the risk of gastric cancer in members of HNPCC families in a gastric cancer endemic population, particularly in younger subjects and mutation carrier families, is high enough to justify careful screening.