Let me tell you how it occurs. The branches of your lungs are lined with small finger like projections called cilia that are constantly moving inhaled particles back out of the lungs. On inhalation of cigarette smoke paralyzes these cilia for five minutes. Continued smoking for years damages these cilia and allows carcinogenic particles to remain in the lungs instead of being removed.
I work in the oncology field and treat lung and many other lung cancers daily.
Now that makes a lot more sense.