Have another cigarette while you ponder this.

DNA mutations

"We've known for many years now that all cancers are due to abnormalities of DNA...that occur in every single cell of the body over the course of a lifetime," said Stratton.

"But although we've known that, it's remarkable how rudimentary our knowledge is about what the processes are that cause these abnormalities, these mutations in our DNA."

"What we believe...is that sometimes in normal cells...this stops functioning properly and over-functions. It causes too many mutations and the accumulation of those mutations pushes the cell along the line to become cancer."

Read more @ http://www.foxnews.com/health/2012/05/17/study-unpicks-gene-changes-behind-breast-cancer/

Indeed, tobacco accounts for 87 percent of all lung-cancer deaths. But the same ailment is not exactly rare among nonsmokers: As many as 24,000 Americans who never puffed a cigarette die each year from the illness, the American Cancer Society reports.

The American Cancer Society estimates that 3,400 nonsmoking adults die annually from exposure to secondhand smoke.

But it is radon gas – an odorless, radioactive, element rising from uranium deposits and collecting inside homes – that leads to most of the lung cancers that strike down nonsmokers. According to the U.S. Environmental Protection Agency, radon kills 20,000 Americans annually.

Men who have never torched a cigarette, cigar or pipe have higher death rates than female non-smokers, cancer experts have learned. But there’s an epidemiological flipside to that stat: At ages 60 and above, there are twice as many female nonsmokers as males who never picked up the habit, yet more nonsmoking women are affected by lung cancer, says the American Cancer Society.

http://vitals.msnbc.msn.com/_news/2012/05/18/11759180-donna-summer-one-of-thousands-of-nonsmokers-killed-annually-by-lung-cancer?lite