Thank you. That's an excellent question.
I think Dr. Stephen Lam will outline more of an answer to your question. The best evidence we have for decreasing mortality in people at risk of lung cancer is in people aged 55 to 74 with a significant smoking history, with something that we call “pack-years”, such as 30 pack-years. If you smoked for 30 years at a pack per day, and if you had not quit within 15 years prior to being screened, that's the population where we know most about it. When you look at the ability to detect cancer and what's cost-effective, you might start older; you might start with a higher smoking exposure; you might also add in certain risk factors. I think Stephen will take you through some of the recommendations, but I think the age currently, at the youngest, would be 55.
There are a lot of questions, such as, ““What if I didn't smoke?”, or “What about people with a family history and other occupational exposures?” Currently, the best evidence for that comes from some work done by Martin Tammemägi, a Canadian. He has published a risk calculator, which we can certainly forward to people so they can calculate their risk, but currently the best evidence is in that age group of 55 to 74 with a significant smoking history.
Paul, do you want to add anything to that?