Risk of Gastric Cancer is Highly Dependent on Type of First-Degree Family Member Affected by Cancer: Lessons from a High-Risk Population in Iran

Background: Family history of gastric cancer (GC) in first-degree relatives may increase the risk of GC. This study aimed to assess how family history of GC in first-degree relatives really affects the risk of GC in an extremely high-risk population. Methods: A large population-based case-control study was carried out on 1222 incident GC cases and 1235 controls in Ardabil Province-a high-risk area in North-West Iran-to assess the associations of GC family history in first-degree relatives with the risk of GC (2003-2017). Results: GC family history did not significantly associate with the risk of GC overall (ORadj=1.09, 95% CI: 0.80-1.47, P=0.589). It found no significant association of GC family history in a parent, and in a father, mother, and sister separately, with the risk of GC. However, GC risk was significantly associated with a history of GC in a sibling (ORadj=1.61, 95% CI: 1.11-2.35, P=0.013), especially brother (ORadj=2.24, 95% CI: 1.41-3.64, P=0.0008). The risk was greatly increased in subjects with two or more affected brothers (ORadj =5.56, 95% CI: 2.33-14.20, P=0.0002). Conclusion: We did not find a familial tendency to cardia GC and non-cardia GC as well as histopathologic features. Determining the type of first-degree relationships with GC may, therefore, be more important than assessing family history alone for predicting the risk of GC in this high-risk area.