Radiation and all that:

A significant excess of breast cancer was found among female workers exposed to radiation; concentration of the excess risks to primary sites sensitive to radiation suggests that ionising radiation during flights may add to the cancer risk of all flight personnel. Female cabin attendants had a significant 1.9-fold incidence of breast cancer and a 15-fold incidence of bone cancer compared with the national average.
source: BMJ 1995;311:649-652 (9 September)