Risk of breast cancer is also increased among retired US female airline cabin attendants

EDITOR—An excess incidence of breast cancer has been reported among Finnish1 and Danish2 airline cabin attendants (standardised incidence ratio 1.9 (95% confidence interval 1.2 to 2.2) and 1.6 (0.9 to 2.7) respectively). In a retrospective cohort survey of retired flight attendants from one US airline we also found an excess incidence of breast cancer (standardised incidence ratio=2.0 (1.0 to 4.3)) (unpublished data).

Neither of the previous reports identified a cause for this excess incidence. One suggested that, on the basis of estimated exposures, radiation could account for an excess incidence of only 10%.1 Another study said that radiation could be responsible for the excess by acting as a cancer promoter but provided little corroborating evidence.3

We suggest that exposure to dicophane (DDT), an organochlorine pesticide used to rid airplanes of insects in the 1950s to 1970s, may be a risk factor for breast cancer. According to a recommendation by the World Health Organisation, on certain international flights DDT was to be sprayed throughout the aircraft from a single use, hand operated aerosol dispenser by a flight attendant after the doors were closed before takeoff, while air ventilation was limited. This may have resulted in substantial inhalation and dermal exposure to DDT for the person operating the aerosol.

Several population based studies have investigated DDT as a risk factor for breast cancer and obtained mixed results.4 Using a case-cohort analysis we assessed whether flight attendants with high exposures to DDT might be more likely to have breast cancer. For comparison we assessed whether those who had made more flights in their career—a proxy for exposure to cosmic radiation—might be more likely to have breast cancer. We asked the flight attendants to tabulate by year the number of flights on which they flew and the number of flights on which they sprayed pesticides. Those with breast cancer were more likely to have had higher than median exposures to DDT than those without breast cancer (odds ratio 2.2 (0.4 to 10.9)). A much weaker and slightly protective association was found between breast cancer and number of flights flown (odds ratio 0.8 (0.2 to 3.5)). Although other risk factors for breast cancer were not adjusted for, the effect size of these confounders in other studies is insufficient to explain the excess we observed.

Our preliminary data are consistent with previously reported excess incidences of breast cancer among flight attendants. Furthermore, they support the hypothesis that exposure to DDT may be a risk factor for breast cancer. More carefully designed studies are needed to resolve these unusual and consistent findings.