Cancer cells, as imagined in 3-D software. (iStock)

Scientists have long agreed that a person's risk of getting cancer comes down to a mix of genes, lifestyle, environment thrown in with some measure of chance. But the relative importance of each factor has never been settled.

In early January, a team of researchers from Johns Hopkins Medicine caused a stir when they published a study in the journal Science detailing their "bad luck" hypothesis for how normal cells turn bad. Their work involved trying to figure out why tissue in certain parts of our bodies are more vulnerable to developing cancer than others and they concluded it had to do with how many times they divide -- a process that occurs somewhat at random.

The researchers described it as analogous to getting into a car accident. Just as your risk of getting into a crash goes up the longer the duration of the trip, your risk of cancer goes up as you age. The weather, the condition of the engine, whether you've had enough sleep, and other external factors can make things better or worse. But in the end, they said, whether you have an uneventful trip or a disastrous is one of chance. All in all, they calculated that bad luck could lead to up to 65 percent of cancers.

White it certainly wasn't the authors' intent, some cited the study as a reason to call it quits on efforts they were making to have a better diet or avoid environmental pollutants. If they were doomed anyway by chance, why bother?

A paper out this week in Nature has the opposite message. Led by a team at Stony Brook, the research used four approaches, including stem cell experiments, computer modeling and molecular "fingerprinting" of cancers, to conclude that the vast majority -- 70 to 90 percent -- of your lifetime cancer risk could be due to external factors.

In the stem cell tests, the group studied how they divide in the various parts of the body. They thought they would find that those with similar patterns of division would have similar risk for the disease. It turned out to not be true, an outcome that suggests that some external factors play a role. They also looked at how cancers change according to where people live like when people move from a low-risk area to a high-risk area and take on the risk of the high risk area -- which seems to imply that something in the environment or lifestyle of that new place impacts the risk.

"People cannot hide behind bad luck," Yusuf Hannun, director of Stony Brook, told BBC News. "They can't smoke and say it's bad luck if they have cancer. It is like a revolver, intrinsic risk is one bullet."

Kevin McConway, a professor of applied statistics at the Open University, said in an interview with the Telegraph that the study suggests the astounding idea that if we could somehow "magic away" all those external factors, some 70 to 90 percent of cancers would not occur. However, McConway didn't think we should rule out chance just yet.

"Even if someone is exposed to important external risk factors, of course it isn’t certain that they will develop a cancer – chance is always involved," he said.

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