Why? What can possibly change at the cellular level to affect the body 25 years later? And how can they blame it on smoking and not, say, air pollution or Three Mile Island?
I'm not saying smoking doesn't cause it, I'm drilling down here.
Why don't you ask someone who 25 years ago used to work in an asbestos mine about long lag periods? They are common for many types of cancers. If your lungs are coated with tar from smoking, they just don't become uncoated 25 years later. You still have large amounts of carcinogens in you, and they can cause cell damage at any time.
And how can they blame it on smoking and not, say, air pollution or Three Mile Island?
Because researchers can screen for air pollution or three mile island. If you were to take two identical populations -- say 50,000 people who never smoked and 50,000 people who smoked for 10-20 years and then quit 25 years ago -- and you normalize both populations for differences in likely exposure to air pollution and radiation, you'll still see an increase in lung cancer rates in the smoker group. This is how studies are done, and they can conclusively pinpoint smoking.
There are viruses that hide (that is a euphemism) for sometimes years, before their true impacts manifest themselves. Sometimes for many years.
Examples.........