Much has been written about pesticides and pollutants as being major contributors to cancers today. According to the National Toxicology Program at the U.S. Department of Health and Human Services, there are 52 chemicals known to contribute to cancers of all kinds in humans and 176 chemicals reasonably anticipated to be human carcinogens. Lung and mammary cancers are the most common types of cancers that are found in animal based studies of potential carcinogens. Despite this data, most experts believe that more relevant environmental risks involve diet, lifestyle, and factors related to a prolonged exposure to estrogens. However, a brief discussion of some proven and unproven chemicals associated with breast cancer risk is worthwhile.
Smoking: Researchers from Albert Einstein College of Medicine in New York examined the association between cigarette smoking and incidence of breast cancer in a cohort of women who had smoked for up to 40 years. The women were subsequently followed for an average of 10.6 years. Their risk of breast cancer was 60% higher than that of women who had never smoked. Among those who smoked 20 cigarettes or more a day for 40 years, the increased risk rose to an 83% increase.
DDT: DDT and its metabolite DDE are weakly estrogenic organochlorine pesticides that accumulate in the food chain and collect in human adipose tissues through the consumption of animal products. Although several studies showed no link when blood DDT levels were checked many years after exposure, a recent study based on samples from blood collected during perinatal periods showed that women heavily exposed to the pesticide DDT during childhood are five times as likely to develop breast cancer later in life.
Other Pesticides: Other pesticides including endosulfan, toxaphene and dieldrin have been implicated as causing breast cancer based on animal studies, but their contribution to human breast cancer is unclear.
Commercial Product Chemicals: A long list of chemicals found in common commercial products have been implicated in breast cancer. This list includes industrial solvents (trichloroethylene, toluene and benzene), plastic water bottles and baby bottles (bisphenol-A), and polyvinyl chloride, a ubiquitous chemical found in food packaging, medical products, appliances, cars and toys. Again, the significance of their contribution to human breast cancer is unclear.
Pollutants: A very well studied group of chemicals collectively called polycyclic aromatic hydrocarbons (PAHs) have also been implicated in breast cancer. The most common sources of these chemicals include charbroiled meat, cigarette smoke, car exhaust, and burning fuel.
Radiation exposure: Mounting evidence suggests that X-ray and gamma-ray exposure may be a significant and causative factor, particularly if the exposure is during childhood or early adulthood. Radiation therapy done for Tuberculosis and dermatologic conditions and radiation exposure from atomic bombs have been proven to cause breast cancer. The most important factor in radiation exposure is the dose of radiation. This is why efforts have been made to decrease the radiation from mammograms by 10-fold. The energy level of the radiation may also be important. Several epidemiologic studies have shown an increased risk of breast cancer among female airline attendants (1.9 fold increased risk). The likely cause for airline attendant’s increased cancer risk is exposure to cosmic radiation (neutrons and gamma rays), which have much higher energy than X-rays.