Environmental cancers still a wild card
— Dr. Karl Kelsey, MD, MOH, is Professor of Community Health and Pathology and Laboratory Medicine at Brown University. He is Director of the Center for Environmental Health and Technology, home to the Brown University Superfund Basic Research Program. Any views expressed here are his own.–
What are we to make of the 250-page report from the President’s Cancer Panel on environmental cancer risk?
Is it a wakeup call for regulators, demanding that they protect us from massive numbers of untested chemicals? Is it an unbalanced, provocative account that ignores the well-known, preventable causes of cancer?
Given the diverse and pointed reactions, the report is almost certainly part overstatement.
Yet, there is also some hard reality that demands a close look and significant improvement in the way we regulate and, therefore, protect ourselves and our children from environmental carcinogens (and toxicants in general).
Although science has taken us very far in understanding how cancers arise, we are fundamentally ignorant of some of the most basic steps that drive the process.
Cancer is a complex disease, resembling more the mystery of the human developmental process than the infectious or degenerative process of a chronic disease.
In fact, cancer is not one disease, but many diseases with different causes, only some of which are understood.
Even if we lack complete understanding, observational studies of exposed populations have provided us with the strongest evidence of whether an exposure is a “cause” of cancer.
Although it could be a case in which people who get these diseases are simply unlucky, it may also be that there are risk factors that we simply do not understand, have not studied extensively, or have even discovered.
It must be recognized at the outset that the President’s Cancer Panel has been asked to provide guidance in this difficult setting of uncertainty.
Let’s start with the facts. The report contains many that are startling and important. For instance, there are “more than 80,000 chemicals in use in the United States” and only “several hundred” have been tested for their ability to cause cancer.
In this age of computer modeling and simulation, we still cannot predict with certainty which chemicals will be carcinogens. To know if something is a carcinogen, we need to run tests.
Even then, we cannot be certain how humans will respond, but the data provides an assessment. Even in the best of circumstances, we only test single chemicals, and although these tests are useful, people are rarely exposed to only one chemical.
Rather, we are exposed to mixtures of chemicals, and we do not yet test mixtures.
Consequently, we don’t know the carcinogenic potential of thousands of chemicals.
This does not mean that there are thousands of carcinogens in our environment; it means that we don’t know about the chemicals and chemical mixtures in our environment.
The report mentions preventable causes of environmental cancer — including radiation, air and water pollution, and known carcinogenic solvents — and provides practical advice for the public to reduce their everyday exposures.
These are important, known cancer causes, and the Panel is right to emphasize that we must do a better job protecting people from these understood dangers.
One point the Panel does not make is that the growth of the global economy is resulting in the export of known carcinogens to the developing world.
One example: although we have not banned asbestos in the United States and exposures have been diminishing over time, asbestos is still mined and widely used in India, China and the developing world.
These areas will likely experience an epidemic of lung cancer, mesothelioma, and asbestosis that is preventable.
The United States is the largest player in a global economy, and observations such as this belong in a report to the President.
The report has been criticized for not stressing what some would term the most important causes of cancer: tobacco, obesity, alcohol, infections, hormones, and sunlight.
There is some merit to this criticism, of course, but it is equally important to remember that attempting to restrict our understanding of a disease as complicated as cancer to a short list is, well, short-sighted. For example, asbestos interacts with tobacco smoke to multiply the risk of lung cancer.
Similarly, arsenic in drinking water has been linked to bladder cancer, and this risk may be more prominent in smokers.
In addition, much of the data we have on the major causes of cancer come from studies of adults.
We do not yet know how exposures in early life to these known cancer risk factors, as well as emerging environmental factors, affect our cancer risk later in life.
We now believe, however, that exposures during this critical period significantly contribute to carcinogenesis.
Uncovering environmental factors that affect the developing human and result in susceptibility to carcinogens later in life is daunting. Yet, it is possible, and even likely, that there are exposures that act in this fashion.
We are beginning to understand what these exposures might be, and candidates include those that mimic hormones and other chemicals that act like biological mediators.
Urging action to prevent cancer where we know the cause and how to prevent it, such as tobacco use, is important, but we should also recognize that the science must move ahead in order for us to understand which chemicals are safe to use and which need to be regulated.
This can be done by vigorously supporting stronger science targeting environmental carcinogens.
This research goes hand in hand with prudent, economically friendly, technology forcing regulatory reform.
Neither will be accomplished overnight. The President’s Panel, with deliberate intent, has focused our attention in the right place.
(Doctors Brock Christensen and Carmen Marsit of Brown University contributed to this article.)
Photo shows the New York City skyline behind part of a chemical plant at Port Elizabeth, New Jersey, May 27, 2005, in an area nicknamed “The most dangerous two miles in America.”