No, Cancer is Not Mostly Bad Luck - The Role of Environmental Factors

No, cancer is NOT mostly bad luck. We've set the record straight in Science magazine (Ashford et al, 6 February 2015) after it published an article and accompanying editorial so full of misstatements that scientists around the world, including myself, felt compelled to correct the record with the facts. (See Science 2 January 2015 study by Drs. Tomasetti and Vogelstein and accompanying "bad luck of cancer" editorial by Jennifer Couzin-Frankel, with subsequent "backlash" editorial here).

Our letter to the editor of Science not only challenges the misstatements of the reports that most cancers are due to 'bad luck', but points out that such misstatements dangerously undermine successful efforts to prevent cancers. Many cancers are linked to diet, lifestyle factors, alcohol, tobacco, sexual activity, and environmental factors. There is overwhelming evidence that cancer and other life-threatening diseases can be prevented by improving diet and lifestyle habits, and limiting harmful exposures to environmental factors including some chemicals like formaldehyde and diesel exhaust, asbestos, some viruses, alcohol, radiation, and second hand smoke. People are exposed to carcinogens at work, home, school, and recreation areas. For example, there are cancer-causing chemicals in household products, building materials, personal care products, food and food additives, tobacco products, industrial emissions, and vehicle exhaust. Carcinogens contaminate air, waterways, land, wildlife, and our bodies. Many of these can be replaced by safer materials or eliminated altogether, thereby reducing environmental releases and harmful human exposures.

In addition to cancer, exposure to harmful chemicals can lead to learning and behavioral impairments, developmental delays, reproductive harm, and chronic diseases including autoimmune disease, asthma, and obesity. The important work of preventing these health harms can only be done if we increase our efforts to identify the causes - including industrial and environmental pollutants - and reduce or replace them to prevent harmful exposures.

The study in Science by Tomasetti and Vogelstein reports that the more times a cell divides, the more opportunities there are for random mutations of the DNA, and therefore the more risk that the tissue may get cancer over a lifetime. As we wrote in our response to Science, "it is widely acknowledged that many cancers can be explained by a two-step process: initiation by one or a series of DNA mutations, followed by the promotion of the genetic "mistake" to a recognizable tumor or blood disease. The observation that replication of the mistake may proceed at different rates in different tissues is no doubt correct."

However, the authors over-step their own observations and err when they suggest that random mutations (or 'bad luck') are "the major contributors to cancer overall, often more important than either hereditary or external environmental factors." This is simply wrong. First, it incorrectly conflates differences in mutation rates between tissues and organs in the body, to differences in cancer risks between people across populations. Second, it fails to note the overwhelming scientific evidence that many mutations are initiated by harmful exposures to toxic chemicals, viruses, or radiation.

The 'bad luck' assertion is so wrong-headed that the International Agency for Research on Cancer (IARC), the World Health Organization's specialized cancer agency felt compelled to issue a public statement that it "strongly disagrees" with the conclusions of Tomasetti and Vogelstein. "IARC experts point to a serious contradiction with the extensive body of epidemiological evidence as well as a number of methodological limitations and biases in the analysis presented in the [Tomasetti and Vogelstein] report." Fifty years or more of epidemiologic research around the world has demonstrated that the risk of certain cancer types is much greater in populations exposed to specific carcinogenic chemicals and industrial pollutants - and, we can reduce the burden of cancer if we reduce our use of them.

The article by Drs. Tomasetti and Vogelstein may explain why the lung is more at risk for cancer than the pelvic bone, but it doesn't tell you anything about why one person gets lung cancer and another doesn't. But, we know it isn't just bad luck! That's where environmental triggers such as chemical pollution are important. For example, IARC and the World Health Organization identified outdoor air pollution as a cause of lung cancer, and also linked it to an increased risk for bladder cancer (IARC 2013). "The air we breathe is filled with cancer-causing substances," said Kurt Straif, PhD, head of the IARC Monographs Section. "Outdoor air pollution is not only a major environmental risk to health in general, it is the most important environmental cancer killer due to the large number of people exposed." These are cancers we can prevent, and that often hit hardest economically stressed communities of color near polluting industries. See for example my 2013 blog of a Toxic Tour of Southwest Detroit, where the cancer rate is higher than the national average, and highest among predominantly African-American communities in Detroit.

As Dr. Ted Schettler, MD, MPH, noted in his critique of Tomasetti and Vogelstein's study, "Cancer trends in specific tissues over decades make clear that environmental factors are deeply involved. By drawing conclusions that go beyond their data, the authors may deflect attention from the critical need to expand public health cancer prevention programs in our homes, communities, and workplaces. That would truly be an unfortunate outcome."

Dr. Adam Finkel, ScD, MPP a public health expert at the University of Pennsylvania and co-author of our letter in Science, provided this analogy: "Imagine a study that laboriously proved this ho-hum finding: 'most of the differences between the rate of fatal traffic accidents on US roads can be explained by the fact that roads with lots of cars on them kill more pedestrians than sparsely-used roads.' Now suppose your child ran after a ball, onto a quiet street, and ran back into your yard with no ill effects. But the same day, a friend's child ran onto an interstate highway and was killed. Would you tell your friend that her child was the victim of BAD LUCK? I hope not."

I agree with Dr. Finkel that, "all Tomasetti and Vogelstein have shown is that things that cause cancer do so more readily in rapidly-dividing tissues than in slowly-dividing ones. Their work sheds no light whatsoever on what causes cancer in either kind of tissue." That's an area worthy of further scientific research.

See our letter in Science at: Cancer risk: Role of environment. Nicholas A. Ashford, Patricia Bauman, Halina S. Brown, Richard W. Clapp, Adam M. Finkel, David Gee, Dale B. Hattis, Marco Martuzzi, Annie J Sasco, and Jennifer B. Sass. Published online 5 February 2015 [DOI:10.1126/science.aaa6246]