Associations between birth season and the anatomic subsites of gastric cancer in Beijing, China.

Birth season is an important risk factor for several cancers; for example, anatomic subsite risk factors for gastric cancer differ substantially by when patients were born. In this population-based retrospective study, we explored the relationship between birth season and gastric cancer of different anatomical sites, focusing on gastric cancer patients who were registered at the Beijing Institute for Cancer Research from 2003 to 2012. In total, 19,668 patients were divided into three groups according to the anatomical site of the primary lesion: cardia (n = 3911), noncardia (n = 5383) and unknown (n = 10,374). The 5383 patients in the noncardia group were further subdivided into the following subgroups: fundus (n = 455), corpus (n = 902), greater curvature (n = 110), lesser curvature (n = 512), antrum (n = 2635), pylorus (n = 106) and overlapping (n = 663). Finally, all gastric cancer cases, the three major groups, and the seven noncardia subgroups were, respectively, compared with inpatients from the Dongzhimen Hospital of Beijing from 2003 to 2013. A logistic regression method with sex and age as control factors was used to evaluate the relationship between birth season and gastric cancer with the level for statistical significance set at P < .05. Taking winter as the reference season, we found people born in summer had a lower probability of developing gastric cancer (summer: odds ratio [OR] = 0.925, 95% confidence interval [CI] = 0.875-0.978, P = .006). Among the three groups, the noncardia group had the lower probability of birth season being spring or summer (spring: OR = 0.917, 95% CI = 0.843-0.997, P = .042; summer: OR = 0.883, 95% CI = 0.810-0.962, P = .004), but the cardia and unknown anatomical groups showed no statistical significance for season of birth (P > .05). Among the seven subgroups, those born in summer were less likely to develop gastric cancer in the antrum and lesser curvature than those born in winter (antrum: OR = 0.861, 95% CI = 0.766-0.968, P = .012; lesser curvature: OR = 0.746, 95% CI = 0.579-0.961, P = .023); the other subgroups showed no significant differences by season of birth (P > .05). This study demonstrated that gastric cancer is related to birth season. For people born in summer, the risk of developing gastric cancer was comparatively lower than for people born in winter. Seasonal differences in immune function and maternal nutrition status during pregnancy may explain these findings; however, further large-scale prospective studies will be required to validate these findings.