Everything would be speculation at this point. There does seem to be a bigger effect on women. We do know that if you took a population of non-smoking women and a population of non-smoking men, there would be more lung cancer in the non-smoking women. It might be that being female is, in and of itself, a risk factor for developing lung cancer, and that might be a genetic thing. There are lots of different ways that could go.
Also you have to think about this in the context of what the temporal trends were in smoking over the period of the analyses. Men took up smoking earlier and stopped smoking earlier on sort of a population scale. Women took it up later and stopped smoking later, so we're definitely seeing some of that interaction between smoking and radon in that upward trend. We do hope that over time it will plateau and start to come down again, and we'll keep paying attention in B.C. to evaluate whether or not that happens.
There's also the question of other environmental lung carcinogens. What is the interaction between radon and diesel exhaust? We don't know. What is the interaction between radon and something like asbestos or another lung carcinogen? We just don't know. There are all of these things happening in the environment and your lungs are the first things that the environment comes in contact with, so it's quite possibly interaction between radon and other stuff as well.