• asthma;
  • hayfever;
  • prostate cancer;
  • risk;
  • men

Inflammation, and more generally, the immune response are thought to influence the development of prostate cancer. To determine the components of the immune response that are potentially contributory, we prospectively evaluated the association of immune-mediated conditions, asthma and hayfever, with lethal prostate cancer risk in the Health Professionals Follow-up Study. We included 47,880 men aged 40–75 years with no prior cancer diagnosis. On the baseline questionnaire in 1986, the men reported diagnoses of asthma and hayfever and year of onset. On the follow-up questionnaires, they reported new asthma and prostate cancer diagnoses. We used Cox proportional hazards regression to estimate relative risks (RRs). In total, 9.2% reported ever having been diagnosed with asthma. In all, 25.3% reported a hayfever diagnosis at baseline. During 995,176 person-years of follow-up by 2012, we confirmed 798 lethal prostate cancer cases (diagnosed with distant metastases, progressed to distant metastasis or died of prostate cancer [N = 625]). Ever having a diagnosis of asthma was inversely associated with risk of lethal (RR = 0.71, 95% confidence interval [CI] = 0.51–1.00) and fatal (RR = 0.64, 95% CI = 0.42–0.96) disease. Hayfever with onset in the distant past was possibly weakly positively associated with risk of lethal (RR = 1.10, 95% CI = 0.92–1.33) and fatal (RR = 1.12, 95% CI = 0.91–1.37) disease. Men who were ever diagnosed with asthma were less likely to develop lethal and fatal prostate cancer. Our findings may lead to testable hypotheses about specific immune profiles in the etiology of lethal prostate cancer.