What Causes Breast Cancer? Reviewing the IOM Report on BC and the Environment
Earlier this month the IOM issued a big report on breast cancer and the environment. The thick analysis, commissioned and sponsored by the Susan G. Komen for the Cure®, was authored by an expert panel. Their task – to assess all available information on what causes BC, and make recommendations accordingly – was essentially impossible. Some immediately critiqued the work and, perhaps implicitly, the funding – for its failure to yield sharp or clearly-actionable insights into BC causes.
The document starts, blandly, with some straightforward stuff. The recommendations for lifestyle changes seem paternalistic when not obvious. Where the report gets interesting, and offers value, is in considering a few specific environmental toxins that might be causative in the current breast cancer epidemic. While proving that any one (or several) of the chemicals listed below causes BC will be difficult, developing a clear, working list of likely compounds that merit research attention is an important step.
Each year, over 230,000 women in the U.S. develop a breast tumor. The problem, in terms of preventing breast cancer, is that most established risk factors – like being older, later age at menopause, being young at the time of first menstruation and some genetic traits – aren’t amenable to intervention.
For this project, the IOM committee interpreted the term “environment” broadly – it considered all possible causes of BC that aren’t directly inherited through DNA, including factors that might influence a genetic disposition. They looked at a wide range of exposures: “how a woman grows and develops during her lifetime; what she eats and drinks; the physical, chemical, and microbial agents she encounters; how much physical activity she engages in; medical treatments and interventions she undergoes; and social and cultural practices…”
What they found, with my comments interspersed and conclusions:
The most convincing evidence linked BC to hormone therapy with estrogen and progesterins, ionizing radiation (as might occur in medical procedures like CT scans; the amount of radiation in mammography is too low for concern, the committee emphasizes), excess weight (i.e. being fat, or more-than-fat) in postmenopausal women, and alcohol (addressed here, previously).
Where they found no clear link: smoking (surprise! the evidence is limited, they say), personal use of hair dyes, non-ionizing radiation (like that emitted by microwaves and other electrical devices).
On the up side: Physical activity appears to lessen a woman’s breast cancer risk.
Quite a few factors fell into a gray zone, for which “the evidence is less persuasive but suggests a possible association with increased risk.” These are: exposure to secondhand smoke (this might be a cause, but smoking isn’t? seems unlikely, ES), nighttime shift work (steroids/stress effect? Or just too much junk food).
Finally, they name some chemicals: benzene, ethylene oxide, or 1,3-butadiene (these may be present in some workplaces; one might be exposed from breathing auto exhaust, pumping gas, or inhaling tobacco smoke, they indicate) and bipsphenol A (BPA) – one of the “biologically plausible hazards in the environment.” As they indicate, animal data provide clear evidence for a mechanism by which BPA, which is widely-used in plastic containers and food packaging, might cause breast cancer. “But studies to assess the risk in humans are lacking or inadequate.”
The IOM committee study authors consider the difficulties in testing environmental hazards. Of course, as they point out, it wouldn’t be ethical to deliberately expose women to potentially harmful substances in a clinical trial. For this reason, they advocate more research in animals and in vitro systems. But those kinds of experiments are limited, in their words: “they can provide indications that a chemical or other agent may cause harm, but these models are approximations of human experience.”
So we’re stuck with a lot of inconclusive data, and an obvious moral imperative not to systematically test the effects of possible environmental toxins on women who might develop BC. There’s a table posted, with strategies to reduce risk, but it recommends for the most part obvious things, and an annoyingly-toned paragraph:
These actions include avoiding unnecessary medical radiation throughout life, avoiding use of postmenopausal hormone therapy that combines estrogen and progestin, avoiding smoking, limiting alcohol consumption, increasing physical activity, and, particularly for postmenopausal breast cancer, minimizing weight gain. Some of these actions may have additional health benefits beyond their potential contribution to reducing breast cancer risk. In many cases, women can be aided by the actions of others, including their families and health care providers.
(Why don’t they just say: “be a good girl, get rest, and stay slim?”)
The segment on the future and needed research emphasizes the need for research on early-life exposure to chemicals, pre-menopausal obesity, and other factors that may influence development of BC later on in a woman’s life. This makes sense to me.
The most troubling findings have to do with the chemicals. Carcinogens like benzene are hard to put a finger on, when it comes to causing cancer in a population where cars are abundant and oil leaks often, and occasionally abundantly, into large gulfs of water. The BPA issue is a genuine concern, with little clear data in humans. Until those data are evident (which, if it takes decades to show the effects on youngsters exposed who develop BC in, say, their 40s), will not be for a while – you have to wonder if doctors should recommend more drastic steps to avoid routine exposure to and ingestion of potentially toxic chemicals.
If you’d like to read about this report and some of the concerns about chemicals that might cause BC, I recommend this post by Julia Brody, of the Silent Spring Institute.