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Long-term deleterious effects of repeated blood donations may be masked by the donors' healthy life- style. To investigate possible effects of blood donation and iron loss through blood donation on cancer incidence while minimizing "healthy donor effects," we made dose-response comparisons within a cohort of Swedish and Danish blood donors. We used a nested case-control study design, in which case patients were defined as all donors who were diagnosed with a malignancy between their first recorded blood donation and study termination (n = 10866). Control subjects (n = 107140) were individually matched on sex, age, and county of residence. Using conditional logistic regression, we estimated relative risks of cancer according to number of blood donations made or estimated iron loss 3-12 years before a case patient was diagnosed with cancer. All statistical tests were two-sided. No clear association was observed between number of donations and risk of cancer overall. However, between the lowest (~median, <0.75 g) and highest (>90th percentile, >2.7 g) categories of estimated iron loss, there was a trend (P~,Ofld < .001) of decreasing risk for cancers of the liver, lung, colon, stomach, and esophagus, which are thought to be promoted by iron overload (combined odds ratio [OR] = 0.70, 95% confidence interval [Cl] = 0.58 to 0.84), but only among men and only with a latency of 3-7 years. The risk of non-Hodgkin lymphoma was higher among frequent plasma donors (>25 vs 0 donations, OR = 2.14, 95% Cl = 1.22 to 3.74). Repeated blood donation was not associated with increased or decreased risk of cancer overall. The lack of consistency across latency periods casts doubt on an apparent association between reduced cancer risk and iron loss in men. The positive association between frequent plasma donation and risk of non-Hodgkin lymphoma deserves further exploration. [ABSTRACT FROM AUTHOR]

Background Blood transfusions may influence the recipients' cancer risks both through transmission of biologic agents and by modulation of the immune system. However, cancer occurrence in transfusion recipients remains poorly characterized. Methods We used computerized files from Scandinavian blood banks to identify a cohort of 888843 cancer-free recipients transfused after 1968. The recipients were followed from first registered transfusion until the date of death, emigration, cancer diagnosis, or December 31, 2002, whichever came first. Relative risks were expressed as ratios of the observed to the expected numbers of cancers, that is, standardized incidence ratios (SIRs), using incidence rates for the general Danish and Swedish populations as a reference. All statistical tests were two-sided. Results During 5652918 person-years of follow-up, 80990 cancers occurred in the transfusion recipients, corresponding to a SIR of 1.45 (95% confidence interval [CI] = 1.44 to 1.46). The SIR for cancer overall decreased from 5.36 (95% CI = 5.29 to 5.43) during the first 6 months after transfusion to 1.10 or less for follow-up periods more than 2 years after the transfusion. However, the standardized incidence ratios for cancers of the tongue, mouth, pharynx, esophagus, liver, and respiratory and urinary tracts and for squamous cell skin carcinoma remained elevated beyond 10 years after the transfusion. Conclusions The marked increase in cancer risk shortly after a blood transfusion may reflect the presence of undiagnosed occult cancers with symptoms that necessitated the blood transfusion. The continued increased risk of tobacco- and alcohol-related cancers suggests that lifestyle and other risk factors related to conditions prompting transfusion rather than transfusion-related exposures per se are important to the observed cancer occurrence in the recipients. [ABSTRACT FROM AUTHOR]