Risk factors for breast cancer, including occupational exposures

Lifestyle-Related Risk Factors for Breast Cancer

Use of exogenous hormones

According to the International Agency for Research on Cancer (IARC), in-utero exposure to diethylstilbestrol, i.e., when a pregnant woman uses the drug, increases a female child’s risk of developing breast cancer.


The knowledge on the etiology of breast cancer has advanced substantially in recent years, and several etiological factors are now firmly 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.

For breast cancer the following substances have been classified 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 classified as a Group 1 carcinogen, although the evidence for carcinogenicity in epidemiologic studies, and specifically for the human breast, is limited.

The classification “probably carcinogenic to humans” (Group 2A) includes estrogen hormone replacement therapy, tobacco smoking, and shift work involving circadian disruption, including work as a flight attendant. If the association between shift work and breast cancer, the most common female cancer, is confirmed, shift work could become the leading cause of occupational cancer in women.


  • Full study (free access) : Risk Factors for Breast Cancer, Including Occupational Exposures, Saf Health Work, NCBI PubMed PMC3431884, 2011 Mar.
  • Featured image credit cipherpharma.

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