Life really is unfair. Some 20,000 people a year with lung cancer, and they've never even tasted the butt of a cigarette. Even more unfair: no one knows why (and it's probably beyond second-hand smoke...).

That's the observation reported in the San Francisco Chronicle late last week, in a survey of oncologists detailed to research on incidences of lung cancer. There's also another layer of unfairness laid onto the story: "women are particularly at risk" of contracting lung cancer, even in the absence of cigarette smoke.

This observation is quite stark in Asian countries, where very few women smoke, observes Stanford University School of Medicine's Dr. Heather Wakelee. For example, about a third of lung cancer cases in Singapore are in nonsmokers, "and most of those are women".

Current research into lung cancer in both women and nonsmokers is relatively new, which means there's no hard data or firm theories to explain this. Aside from the decried culprit, second-hand smoke, other potential causes of nonsmoker lung cancer include industrial chemicals, environmental pollutants, radon gas, and possibly cell proteins that mutate and increase the risk of lung cancer.

There we go: lung cancer doesn't only come from cigarettes. This writer doesn't light up, although he does hang with smokers - but he's almost just at risk of getting lung cancer as the next guy smoking.