Risk of breast cancer in female flight attendants: a population-based study (Iceland)

Objectives: To study whether increased cancer risk, particularly of cancer types previously related to radiation, was found among cabin attendants, us ing employment time as a surrogate of exposure to cosmic radiation. Methods: A cohort of 1690 cabin attendants, 158 men and 1532 women from the Icelandic Cabin Crew Association and two airline companies in Iceland, was established. Cancer sites were ascertained between 1955 and 1997 by follow -up in a cancer registry. The personal identification number of each subjec t was used in record linkage to population-based registers containing vital and emigration status, reproductive factors and histologically verified ca ncer diagnosis. Standardized incidence rates (SIR) of different cancer site s in relation to employment time and year of hiring were calculated, as wel l as predictive values of breast cancer risk for evaluating possible confou nding due to reproductive factors. Results: The total number of person-years was 27,148. Among the women, 64 c ancers were observed whereas 51.63 were expected (SIR 1.2, 95% CI 1.0-1.6), and significantly increased risk for malignant melanoma (SIR 3.0, 95% CI 1 .2-6.2) was found. Significantly increased risks of overall cancers (SIR 1. 3, 95% CI 1.0-1.8) and breast cancer (SIR 1.6, 95% CI 1.0-2.4) were observe d among the female cabin attendants when 15 years lag time was applied. Tho se hired in 1971 or later had the heaviest exposure to cosmic radiation at a young age and had significantly increased risk of overall cancer (SIR 2.8 , 95% CI 1.4-4.9) and breast cancer (SIR 4.1, 95% CI 1.7-8.5). Predictive v alues calculated on the basis of reproductive factors among the cabin atten dants and the population, and risk of breast cancer were 1.0 for parous vs. nulliparous, 1.0 for number of children, and 1.1 for age at birth of first child. Conclusion: The increased risk of breast cancer and malignant melanoma amon g cabin attendants seems to be occupationally related. The part played by o ccupational exposures, i.e. cosmic radiation, disturbance of the circadian rhythm, and electromagnetic fields or combination of these factors in the e tiology of breast cancer among the cabin crew, is still a puzzle as confoun ding due to parity appears to be ruled out. The relationship between the su nbathing habits of the cabin crew and the increased risk of malignant melan oma needs to be clarified. There is also an urgent need to elucidate the im portance of these findings for today's aviation.