Allergies and the Subsequent Risk of Cancer among Elderly Adults in the United States.

BACKGROUND: Allergic conditions may prevent some cancers by promoting immune surveillance. We examined associations of allergic rhinitis, asthma, and eczema with cancer risk among elderly Americans.
METHODS: We used Surveillance Epidemiology and End Results (SEER)-Medicare linked data to perform a case-control study. Cases were individuals with first cancer diagnosed in SEER registries (1992-2013, ages 66-99; N = 1,744,575). Cancer-free controls (N = 100,000) were randomly selected from Medicare and matched on sex, age, and selection year. Allergic conditions were identified using Medicare claims, and logistic regression was used to estimate adjusted ORs (aOR) with significance gauged with a Bonferroni P cutoff (P < 0.00034).
RESULTS: Allergic rhinitis, asthma, and eczema were present in 8.40%, 3.45%, and 0.78% of controls, respectively. For allergic rhinitis, strong inverse associations (aORs, 0.66-0.79) were observed for cancers of the hypopharynx, esophagus (squamous cell), cervix, tonsil/oropharynx, and vagina/vulva. More modest but significant inverse associations were noted for cancers of the esophagus (adenocarcinoma), stomach, colon, rectosigmoid/rectum, liver, gallbladder, lung, uterus, bladder, and miscellaneous sites. Associations were stronger in analyses requiring a dispensed medication to confirm the presence of allergic rhinitis. Asthma was associated with reduced risk of liver cancer [aOR 0.82; 95% confidence interval (CI), 0.75-0.91], whereas eczema was associated with elevated risk of T-cell lymphoma (aOR, 4.12; 95% CI, 3.43-4.95).
CONCLUSIONS: Inverse associations with allergic rhinitis are present for multiple cancers and require etiologic investigation. IMPACT: Understanding of mechanisms by which allergic conditions reduce cancer risk may advance cancer prevention and treatment. ©2019 American Association for Cancer Research.