Not all smokers experience early mortality, and a small proportion manage to survive to extreme ages, research shows. Using long-lived smokers as their phenotype, the authors of a study identified a network of SNPs (a DNA sequence variation occurring commonly within a population) that allow certain individuals to better withstand environmental damage (like smoking) and mitigate damage. Collectively, these SNPs were strongly associated with high survival rates.

Source: Smoking doesn't always mean a shortened life span or cancer