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."

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.

13 ways to help prevent cancer Show all 13 1 /13 13 ways to help prevent cancer 13 ways to help prevent cancer Stopping smoking. This notoriously difficult habit to break sees tar build-up in the lungs and DNA alteration and causes 15,558 cancer deaths a year 13 ways to help prevent cancer Avoiding the sun, and the melanoma that comes with overexposure to harmful UV rays, could help conscientious shade-lovers dodge being one of the 7,220 people who die from it 13 ways to help prevent cancer A diet that is low in red meat can help to prevent bowel cancer, according to the research - with 30 grams a day recommended for men, and 25 a day recommended for women 13 ways to help prevent cancer Foods high in fibre, meanwhile, can further make for healthier bowels. Processed foods in developed countries appear to be causing higher rates of colon cancer than diets in continents such as Africa, which have high bean and pulse intakes 13 ways to help prevent cancer Two servings of fruit and three servings of vegetables a day were given as the magic number for good diet in the research. Overall, diet causes only slightly fewer cancer deaths than sun exposure in Australia, at 7,000 a year 13 ways to help prevent cancer Obesity and being overweight, linked to poor diet and lack of exercise, causes 3,917 deaths by cancer a year on its own Getty 13 ways to help prevent cancer Dying of a cancer caused by infection also comes in highly, linked to 3,421 cancer deaths a year. Infections such as human papilloma virus - which can cause cervical cancer in women - and hepatitis - can be prevented by vaccinations and having regular check-ups 13 ways to help prevent cancer Cutting back on drinks could reduce the risk of cancers caused by alcohol - such as liver cancer, bowel cancer, breast cancer and mouth cancer - that are leading to 3,208 deaths a year 2014 Getty Images 13 ways to help prevent cancer Sitting around and not getting the heart pumping - less than one hour's exercise a day - is directly leading to about 1,800 people having lower immune functions and higher hormone levels, among other factors, that cause cancers 2011 Getty Images 13 ways to help prevent cancer Hormone replacement therapy, which is used to relieve symptoms of the menopause in women, caused 539 deaths from (mainly breast) cancer in Australia last year. It did, however, prevent 52 cases of colorectal cancers 2003 Getty Images 13 ways to help prevent cancer Insufficient breastfeeding, bizarrely, makes the top 10. Breastfeeding for 12 months could prevent 235 cancer cases a year, said the research AFP/Getty Images 13 ways to help prevent cancer Oral contraceptives, like the Pill, caused about 105 breast cancers and 52 cervical cancers - but it also prevented about 1,440 ovarian and uterine (womb) cases of cancer last year 2006 Getty Images 13 ways to help prevent cancer Taking aspirin also prevented 232 cases in the Queensland research of colorectal and oesophagal cancers - but as it can also cause strokes, is not yet recommended as a formal treatment against the risk of 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."

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."