(CNN)-- Ever marvel at someone who smoked and still lived to be 90? Just plain good luck, researchers say. And those who live like Puritans and get cancer anyway?

That's bad luck -- and it's the primary cause of most cancer cases, says a Johns Hopkins Medicine research study.

Roughly two-thirds of cancers in adults can be attributed to random mutations in genes capable of driving cancer growth, said two scientists who ran statistics on cancer cases.

That may sound jaw-dropping. And Johns Hopkins anticipates that the study will change the way people think about cancer risk factors.

They also believe it could lead to changes in the funding of cancer studies, with a greater focus on finding ways to detect those cancers attributed to random mutations in genes at early, curable stages.

Smoking can still kill you

But, no, that's not permission to smoke or to not use sunblock.

Some forms of cancer are exceptions, where lifestyle and environment play a big role. Lung cancer is one of them. So is skin cancer.

And, if cancer runs in your family, this unfortunately doesn't mean you're in the clear. Some cancers are more strongly influenced by genetic heritage than others.

"The remaining third (of cancer cases) are due to environmental factors and inherited genes," the Kimmel Cancer Center said in a statement on the study published Friday in the magazine Science.

Read more:
Random Gene Mutations Primary Cause Of Most Cancer

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