Breast Cancer

Sex and Gender-based Analysis of this topic

Breast cancer is the most common cancer among Canadian women, with more than 23,000 new diagnoses annually [1]. Incidence rose 1% per year from 1969 to 1999 (a 30% increase), but for all age groups, occurrence has since stabilized, albeit at rates that are among the highest in the world [2].

Breast cancer results from a complex, often interactive combination of genetic, hormonal/reproductive and environmental factors [3]. An estimated 5 to 10% of breast cancers are hereditary [4]. ‘Lifestyle’ factors such as diet and alcohol consumption contribute to higher incidence, as does prolonged exposure to one’s own estrogens, resulting from early age at menarche, late age at menopause, late age at first full-term pregnancy or nulliparity [5]. 

In March 2011, a UN scientific meeting concluded that cancers related to the environment comprise approximately 19 per cent of all cancers – nearly one in five [6]. Environment risks include exposures to chemicals and radiation wherever they occur  (home, schools, workplaces), trace elements in personal and consumer products, and/or in the environment-at-large. Individuals are usually involuntary exposed to these environmental risks. 

The most extensive compilation to date on this topic is a U.S. report, State of the Evidence: The Connection Between Breast Cancer and the Environment (Sixth Edition, 2010), which includes references to scientific studies on hormones in pharmaceutical and personal care products, natural and additive hormones in foods, as well as endocrine-disrupting compounds (EDCs) such as Bisphenol A (BPA), phthalates, parabens, aromatic amines, pesticides, herbicides, and heavy metals. Non-endocrine disrupting industrial carcinogens such as benzene and vinyl chloride are additionally covered, as well as light-at-night/melatonin disturbance, and ionizing and non-ionizing radiation [7].
Sex Issues
The overwhelming majority of breast cancers occur in women, with less than 1% occurring in men. The developed female breast comprises more fatty tissue than male breasts, and this tissue attracts and accumulates fat-loving (lipophilic) substances, such as parabens [8], phthalates and other compounds (used, for example, in personal care products) that are linked to breast cancer [9].

The strongest epidemiological evidence linking breast cancer to environmental factors is exposure to ionizing radiation (therapeutic x-rays to treat Hodgkin’s disease, fallout from nuclear explosions, for example). The higher the level of exposure, the greater the risk, with age being a significant factor; younger females are more vulnerable than older ones [10]. Human evidence linking chemicals and breast cancer is mounting, but less clear than exposure to ionizing radiation, partly because of confounding factors, multiple exposures, interactions, and lack of access for researchers to highly exposed and unexposed populations. 

To date, the evidence generally supports an association between breast cancer and polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) [11]. Evidence regarding dioxins and organic solvents also indicate an association [11]. 
Gender Issues
Until recently, occupational research has rarely included women. Occupational studies focusing on breast cancer in males are more common, and results include the possibility of an increased risk in workers exposed to electromagnetic fields and exposure to light at night, which the International Agency for Research on Cancer (IARC) considers a probable carcinogen [12]. On-the-job exposure to pesticides, aromatic hydrocarbons and ionizing radiation also increases risk of breast cancer for males [13]. The occupational evidence that does exist for women shows increased breast cancer risk in two broad areas: a) those who work with toxic chemicals (especially organic solvents) and ionizing radiation, and b) professionals in higher socioeconomic groups, such as teachers and librarians [14]. 
Few breast cancer statistics in Canada include race or ethnicity. In the US, the American Cancer Society offers data on incidence and mortality in white, African American, Asian American, Hispanic/Latina and American Indian/Alaska Native women [15]. Understanding racial/ethnic variations in susceptibility to environmental risk factors for breast cancer is complicated by many variables, including socio-economic status, neighborhood location, home and workplace environments and other exposures. 

Behaviours such as elevated alcohol consumption, lack of physical exercise, poor diet and weight gain - usually referred to as ‘lifestyle factors’ (although they are technically ‘environmental’ but more the result of personal choice, not involuntary exposures) are also linked to increased breast cancer incidence [16].
The connections between breast cancer and ‘the environment’ are neither simple nor universally acknowledged and accepted. Major cancer agencies, including the Canadian Cancer Society, are becoming increasingly open to acknowledging links between cancer and the environment. Given the complexities of these connections, still urgently needed is more emphasis on the precautionary principle and pollution prevention as keys to reversing high breast cancer incidence rates.

A 2007 survey in the journal Cancer reported that 216 synthetic chemicals cause mammary gland tumors in animals and may be implicated in human breast cancer causation [17], signaling possible new directions for epidemiological research. 
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health status > cancer & the environment > breast cancer