When the World Health Organization’s International Agency for Research on Cancer (IARC) announced in May that radiofrequency electromagnetic fields, such as those associated with wireless cellphone use, are “possibly carcinogenic to humans,” a cascade of stories warning of the dangers flooded the media, but few provided details of the report.
One detail was that the IARC classified radiofrequency electromagnetic fields in Group 2b, which includes other common agents as possible carcinogens, such as coffee, gasoline engine exhaust and pickled vegetables. Group 1 agents, which are classified as “carcinogenic to humans,” include chemicals such as arsenic, but also alcoholic beverages and wood dust.
The IARC’s report and the media’s subsequent coverage illustrate the difficulty of connecting environmental agents to cancer.
It is generally believed that cancer is the result of “a complex interaction of genetic and environmental factors,” according to the American Society of Clinical Oncology (ASCO). But only a small number of cancers are hereditary, meaning the majority of cancers are caused by factors outside the body or external factors, such as lifestyle choices (smoking, diet, obesity or alcohol), and other environmental causes, such as exposure to radiation, chemicals and viral or bacterial infections that can damage cells and weaken the immune system.
The task of identifying and proving an environmental factor causes cancer is vitally important, evidenced by the fact that some carcinogens that have been identified and verified have resulted in interventions that have become public health policy. Yet that process often requires many years of scientific research, public debate and policy development, with the media simplifying and sensationalizing complicated and often contradictory findings.
The challenges faced by scientists in studying a suspected carcinogen are particularly difficult, says David Gorski, MD, PhD, managing editor of Science-Based Medicine and a researcher and surgical oncologist at the Barbara Ann Karmanos Cancer Institute in Detroit.
Gorski references tobacco as an example. The first major study definitively linking smoking to lung cancer was published in the Journal of the American Medical Association in 1950. For the next 14 years, scientists continued to study tobacco, moving through the accepted “levels of evidence” required for scientific conclusions.
“The point is, you have to look at the totality of the evidence and synthesize it,” Gorski says. “One study never settles anything.”
At the same time that the scientists were doing their jobs, the issue was being debated in the court of public opinion. It wasn’t until 1964 that Luther Terry, MD, the U.S. Surgeon General, armed with conclusive science, officially declared, “cigarette smoking is causally related to lung cancer in men.” But even though tobacco was officially identified as a carcinogen, it took additional decades of political debate, judicial decisions and advocacy campaigns to finally develop a meaningful public health policy.
“Everybody wants to know the answer about why they got cancer,” Gorski says. “We look for patterns. But patterns often mislead. Especially when you are looking at small numbers.”
It takes a scientific basis along with large numbers and robust statistical analyses “to figure out what we see and what may have general validity,” he adds.
Editor's Note: In upcoming issues, CURE will help readers understand how researchers identify and investigate suspected cancer-causing agents, build their evidence, test their hypotheses and use their findings to suggest interventions that could influence public policy.