Risk factors for breast cancer, including occupational exposures

The knowledge on the etiology of breast cancer has advanced substantially in recent years, and several etiological factors are now fi rmly established. However, very few new discoveries have been made in relation to occupational risk factors. The International Agency for Research on Cancer has evaluated over 900 different exposures or agents to-date to determine whether they are carcinogenic to humans. These evaluations are published as a series of Monographs (www.iarc.fr). For breast cancer the following substances have been classifi ed as “carcinogenic to humans” (Group 1): alcoholic beverages, exposure to diethylstilbestrol, estrogen-progestogen contraceptives, estrogen-progestogen hormone replacement therapy and exposure to X-radiation and gamma-radiation (in special populations such as atomic bomb survivors, medical patients, and in-utero exposure). Ethylene oxide is also classifi ed as a Group 1 carcinogen, although the evidence for carcinogenicity in epidemiologic studies, and specifi cally for the human breast, is limited. The classifi cation “probably carcinogenic to humans” (Group 2A) includes estrogen hormone replacement therapy, tobacco smoking, and shift work involving circadian disruption, including work as a fl ight attendant. If the association between shift work and breast cancer, the most common female cancer, is confi rmed, shift work could become the leading cause of occupational cancer in women