Association Between Allergy, Asthma, and Cancer: The Japan Public Health Center-Based Prospective Study.

Several epidemiological studies have explored the potential associations between allergy, asthma, and cancer incidence, but the findings remain inconclusive. This study investigates the association between a history of allergy, asthma, and cancer risk in a Japanese population. Data were obtained from the Japan Public Health Center-based Prospective Study (JPHC Study). Participants reported in a self-administered questionnaire whether they had been diagnosed by a physician for allergy, asthma, or both (hereafter referred to as "allergy and/or asthma"). They were followed until December 2013. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for overall and site-specific cancers for allergy, asthma, and combined allergy and/or asthma. Subgroup analyses were performed by smoking status. Among participants, 17,679 cancer cases were identified, and 6.5% reported a history of allergy and/or asthma. A borderline association was observed between allergy and/or asthma and thyroid cancer (HR 1.54, 95% CI 1.00-2.35). Subgroup analysis revealed that men with a history of smoking and allergy and/or asthma had an increased risk of colorectal cancer (HR 1.30, 95% CI 1.03-1.63), while never-smoking women with allergy and/or asthma showed an increased risk of cervical cancer (HR 1.98, 95% CI 1.01-3.86). These findings showed no overall association of allergy, asthma, or their combined exposure with cancer risk in a Japanese population, warranting further investigation.