We already know how to stop many cancers before they start, scientists say. However, there is still much to do.
"About half of the cancers could be prevented," said Christopher Wild at the opening session of an international scientific meeting on the environmental causes of cancer in June. Wild is the former director of the World Health Organization's International Agency for Research on Cancer.
"Most of the money goes into cancer biology and treatment," he said, but prevention deserves more attention. "I'm not saying that we should not work to improve the treatment, but we did not properly balance it."
Perhaps no question about cancer is more controversial than its causes. People are wondering and scientists are discussing whether most malignancies are due to random DNA mutations and other random events, or to exposure to carcinogens or behaviors that could be avoided.
At the conference in Charlotte, NC, scientists urged a reassessment of the role of environmental exposures by applying modern molecular techniques to toxicology. They called for a more aggressive collection of examples of human pathology and environmental samples, including water and air, to elucidate the cellular responses to chemicals.
The hope is that by identifying specific traces of exposure in human cancer samples, scientists can identify identifying environmental causes that could be prevented.
"More than 80,000 chemicals are used in the US, but few have been tested for carcinogenic effects," said Margaret Kripke, emeritus immunologist and MD Anderson Cancer Center professor, in an interview at the meeting] "This has been the last A very neglected area of cancer research for decades, "said Kripke, the driving force behind the conference, which was launched by the American Association for Cancer Research. "Environmental toxicology was very popular in the 1
While the frequency of tobacco-related cancers has declined, malignant diseases not associated with smoking are on the increase, Kripke says. Recent evidence suggests an increasing rate of lung cancer in non-smokers. This trend implies other environmental factors.
The overall incidence of cancer is increasing worldwide. This year, 18 million people are diagnosed with cancer and over 9 million are dying.
Infections – many of which are preventable, for example, by human papillomavirus – account for 15% of new cases.
Another increasing cause besides obesity is obesity. As a rule, people move less and eat differently in cities. There, too, the pollution is stronger. "When people move to the cities, the cancer rate increases," Wild said.
One of the biggest obstacles to cancer prevention is that many people simply do not believe that this is feasible. Progress "requires long-term vision and commitment," said Wild. "Financing is limited and there is little private sector investment."
A change in the way in which the benefits of cancer prevention are presented could help. "When I was at the IARC, one thing that impressed me was the power of economic arguments over health arguments to prevent cancer," said Wild.
Cost of cancer treatment can be prohibitive. In Brazil, Russia, India, China, and South Africa alone, the loss of productivity due to premature deaths is $ 46.3 billion a year. "Developing countries are not ready to deal with the rising cancer burden."
The exact proportion of cancers caused by carcinogenic environmental factors and occupational exposure is uncertain. In a report from the President's Cancer Panel in 2009, previous estimates of around 6% were categorized as "outdated" and low. A study by over a hundred concerned scientists in 2015 cited "credible" estimates of 7 to 19%.
Scientists at the meeting in Charlotte highlighted the complexity of the causes of cancer and the need for toxicologists to update methods to reflect this complexity, such as by studying the interactions of environmental and genetic risks and by examining cells after a mixture of exposures , "Most toxic exposures do not occur individually," said Rick Woychik, deputy director of the National Institute of Environmental Health Sciences.
Until recently, many toxicological tests were performed on rodents, as it would be unethical to deliberately evaluate potential carcinogens in humans. But these animal experiments are labor-intensive and slow, he said.
Now new alternatives are tried out. "We learned from pharma that robotics and high-throughput technology can query a lot of biology quickly and at a lower cost," he said.
The epidemiological study of human exposure has been hampered by the difficulty in proving cause-and-effect. Effect – that a given substance actually causes cancer – and inadequacies of survey data from questionnaires.
At the conference, scientists gave insights into new technologies that help fill information gaps.
Bogdan Fedeles from MIT explained how DNA serves as a lifelong "recording device". He and others use duplex sequencing to examine human samples for genetic "fingerprints of exposure".
Allan Balmain, a geneticist at the University of California, San Francisco, spoke about mutational signatures in malignant diseases. For example, these signatures may be a cause of liver cancer, such as smoking, alcohol, or aflatoxin, a mold product that grows on some foods.
Many chemicals that cause or stimulate cancer growth are produced in our bodies. "It's not just about the environment," said Balmain.
Others emphasized a conceptual change in the definition of carcinogens by scientists. Key features may include the ability of a substance to stimulate the growth of malignant cells or cause inflammation – without necessarily causing DNA damage that has long been considered necessary.
"The answer to" What is a carcinogen? "is changing," said Ruthann Rudel, a toxicologist at the Silent Spring Institute who has published extensive information on breast cancer. She described new techniques for studying breast cancer cells for changes in response to certain chemical stresses.
Public health expenditures for the field are high.
Professor Polly Hoppin of the University of Massachusetts, Lowell, discussed the cancer-induced industrial contamination of drinking water at Camp Lejune, NC, in the air pollution at St. John the Baptist Parish, La. And possible exposures to carcinogens from fracking and planned plastic production in Pennsylvania.
Hoppin reflected the US experience of smoking cessation. Scientists knew that smoking caused cancer in the 1950s, she said. Implementing this knowledge required policies and incentives – such as high cigarette taxes and public smoking bans – and took decades.
"Science was not enough," said Hoppin. "How many lives could have been saved if we had acted earlier?"
Elaine Schattner is a medical doctor in New York, writing a book on cancer attitudes, published by Columbia University Press.