Dossier : Cancer : Influence of environmentEnvironmental and occupational causes of cancer: A call to act on what we know
Introduction
We reviewed the scientific evidence, particularly epidemiologic evidence, regarding the contribution of environmental and occupational exposures to the overall cancer burden in the US. The discussion of this evidence has been an area of contention for at least the past three decades, since the assertion in 1977 by Higginson and Muir that 80% of all cancers were due to environmental exposures [1]. The evidence that Higginson and Muir invoked in their seminal article included, “descriptive epidemiological data relating to migrants, geographical variation in incidence, changes in risk over time, correlation studies, clusters and case reports.” Although these authors were referring to “widespread general exposures of air and water pollution, the work environment, exposures resulting from personal choice such as smoking and drinking, and the diet,” the concern that involuntary exposures to substances in the air, water, and work environment are major contributors to cancer in humans has persisted.
Over the past three decades, there have been additional efforts to estimate the proportion of cancer due to these involuntary exposures, including the all too well-known 1981 monograph by Doll and Peto and the more recent reports by the Harvard Center for Cancer Prevention [2], [3]. In this paper, we review the evidence that Doll and Peto and other authors have summarized and their resulting estimates of the proportion of cancer due to various factors. We also provide an alternative interpretation of the evidence and a caution against the very idea of attributing specific fractions or proportions of cancer to particular factors. Next, we summarize our review of the state of the science on the links between certain occupational and environmental exposures and various cancer sites. We conclude with a call for urgent action on what we know or suspect contributes to tens of thousands of excess illnesses and deaths each year in the US alone.
Section snippets
Estimating environmental and occupational contributions to cancer
Over the past few decades, a number of researchers have attempted to estimate the attributable fraction of cancer cases or deaths due to environmental and occupational exposures. Despite these well-intentioned efforts, it has only become more clear that cancers evolve through a complicated web of multiple causes and that it is not only pointless, but also counterproductive to attempt to assign certain exposures a quantitative percentage in the overall burden of cancer. At the same time,
Multi-factorial mechanisms of cancer
Current knowledge of the mechanisms of cancer suggests that all cancers are both environmental and genetic, meaning that there are multiple causes that involve exposures originating outside the body as well as hereditary or genetic changes that converge to produce the disease. One recent description of this dynamic process reduces it to six essential alterations that may overwhelm the natural defenses built into human cells and tissues to produce a tumor [9]. The metaphor these authors use is
State of the science
We summarize the current scientific literature on causes of human cancer from involuntary exposure to physical agents and chemical agents, relying on a combination of reviews of epidemiologic studies of groups of individuals exposed at work or in their communities, and to a lesser extent, on case reports of individual patients exposed to carcinogenic substances and experimental evidence from animal studies as identified in MEDLINE and Google searches of peer-reviewed articles published in
Comments
The scientific literature provides substantial evidence of environmental and occupational causes of cancer and fully justifies accelerated efforts to prevent carcinogenic exposures. In fact, to ignore the scientific evidence is to knowingly permit tens of thousands of unnecessary illnesses and deaths every year. In addition to all of the evidence cited above under “The State of the Science,” we find many other indications that environmental and occupational exposures are linked to cancers.
The
Recommendations
There is substantial evidence that occupational and environmental exposures contribute to the burden of cancer. As a result, there is a compelling need to prevent such exposures wherever feasible. We agree with Sandra Steingraber, author of Living Downstream: An Ecologist Looks at Cancer and the Environment, that the problem is far beyond the demonstrated dangers presented by dump sites, workplace exposures, drinking water, food, or air emissions: “I am more concerned that the uncertainty over
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- Blair A, London S. Personal communication to R. Clapp, January...