Background: In a previous analysis of 12 cancers in the Cancer Prevention Study II (CPS-II) cohort including follow-up from 1982-2000, having both hay fever and asthma was associated with lower colorectal cancer mortality. The combination of these allergic conditions may be a marker for allergy-related immune responses that could inhibit colorectal carcinogenesis. Methods:Weexamined the association of having both hay fever and asthma with colorectal cancer mortality among 1,023,191 participants in CPS-I, followed from 1959-1972, and 1,102,092 participants in CPS-II, now followed from 1982-2008. We also examined associations with colorectal cancer incidence among 174,917 participants in the CPS-II Nutrition Cohort, a subgroup of CPS-II followed from 1992-2007. During the followup, there were 5,644 colorectal cancer deaths in CPS-I, 13,558 colorectal cancer deaths in CPS-II, and 3,365 incident colorectal cancer cases in the CPS-II Nutrition Cohort. Cox proportional hazards regression was used to calculate multivariable-adjusted relative risks (RR) and 95% confidence intervals (CI). Results: RRs for colorectal cancer mortality associated with having both asthma and hay fever, compared with neither condition, were 0.90 (95% CI, 0.74-1.09) in CPS-I, 0.79 (95% CI, 0.69-0.91) in CPS-II, and 0.83 (95% CI, 0.74-0.92) when results from both cohorts were combined in a meta-analysis. The corresponding RR for colorectal cancer incidence in the CPS-II Nutrition Cohort was 0.90 (95% CI, 0.71-1.14). Conclusion: These results support an association between having both hay fever and asthma and modestly lower colorectal cancer mortality. Impact: Research examining other potential markers of allergy-related immune response in relation to colorectal cancer is warranted.
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