Scientists have determined how we can prevent half of all cancer deaths

Imagine a powerful new treatment that could cut all cancer deaths by more than half.

In the age of $10,000-a-month cancer drugs that often extend life by the thinnest margins — a few precious months before the cancer rages back — the idea of such a potent effect sounds like a fantasy.

But it isn't, exactly. A new study published in the journal JAMA Oncology estimates that by applying insights we've had for decades — no smoking, drinking in moderation, maintaining a healthy body weight and exercising — more than half of cancer deaths could be prevented and new cases of cancer could drop by 40 percent to 60 percent.

The excitement, funding and much of the prestige in the fight against cancer is fired up by the immense progress being made in understanding the molecular underpinnings driving the disease. Advances in science have created real hope for new generations of powerful drugs and combination cocktails — along with tremendous hype that almost certainly overstates the amount of progress that is just around the corner. This simple truth remains: Even as science gains powerful insights into many types of cancer, there's still a lot that scientists don't yet fully understand about its sinister biology. Meanwhile, the new study drives home an important point: Scientists already know how to prevent a large swath of cancer deaths.

"Some of the declines we have already seen in cancer mortality — the large decline in lung cancer — that was because of efforts to stop people from smoking," said Siobhan Sutcliffe, an associate professor in the division of public health sciences at Washington University in St. Louis not involved in the research. "Even while we’re making new discoveries, that shouldn’t stop us from acting on the knowledge we already do have."

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To make their estimates of how lifestyle changes could affect cancer's toll on the population, a pair of researchers from Massachusetts General Hospital and the Harvard T.H. Chan School of Public Health used large ongoing studies that have closely followed the health and lifestyle habits of tens of thousands of female nurses and male health professionals. They divided people into two groups: a low-risk group that did not smoke, drank no more than one drink a day for women or two for men, maintained a certain healthy body mass index, and did two-and-a-half hours of moderate aerobic exercise a week or half as much vigorous exercise.

The team compared cancer cases and cancer deaths between the low- and high-risk groups and found that for individual cancers, the healthy behaviors could have a large effect on some cancers: The vast majority of cases of lung cancer were attributable to lifestyle, as well as more than a fifth of cases of colon cancer, pancreatic cancer and kidney cancer.

Then, they extrapolated those differences to the U.S. population at large, finding an even larger proportion of potentially preventable cancer cases and deaths. For women, they estimated 41 percent of cancer cases were preventable and 59 percent of cancer deaths. For men, 63 percent of cancer cases were potentially preventable and 67 percent of deaths.

There are caveats to this — the high-risk group in the study is healthier than the general U.S. population, so there are reasons the numbers may be slightly overestimated. But Mingyang Song, the researcher who led the work, argues the numbers are a good approximation because they may be underestimating the effects of lifestyle, too, because they selected a narrow range of lifestyle factors.

"We should not ignore the knowledge we already learned over the past decade, or the past 100 years," Song said. "We should use this knowledge to move the policy forward and also make the public aware that we already have this knowledge and we can utilize this knowledge, to improve the current cancer prevention effort."

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For years, the fight against cancer has been waged on two related, but largely siloed fronts. At the cutting-edge of science are physicians and researchers with ever more powerful tools to probe how cancer works and invent new ways to stop it. This fight is often waged near the end of the disease, once it has taken hold and doctors and patients would do anything to loosen its grip, even temporarily. On the front lines of public health are researchers who often focus on strategies to reduce deaths by preventing the disease altogether, trying to understand how to screen for it, or what environmental exposures should be avoided.

"There sort of are two worlds, one world focused on therapy and another world focused on prevention, and I do think those two worlds are coming together now," said Tyler Jacks, director of the Koch Institute for Integrative Cancer Research at the Massachusetts Institute of Technology.

This summer, MIT — a place teeming with biologists and engineers who have tended to favor the first approach — will hold a symposium focused on early detection and prevention of cancer. Jacks, who is also a co-chair of the panel of scientists advising Vice President Biden's "Cancer Moonshot," said that prevention and early detection — and even untangling exactly why lifestyle risk factors such as obesity increase risk for cancer — are very much on people's minds.

"There's room for both. Let’s not ignore the power of therapy and its applications for people who have cancer. ... We simply cannot ignore that," Jacks said. "But why can’t we also include, as we think about cancer control more broadly, the lifestyle issues, the human behavior issues, that can lower overall risk."