What percentage of lung cancer is attributable to cigarette smoking?

• A. 40%
• B. 60%
• C. 85%
• D. 95%

Answer: (C)

Smoking is the dominant cause of lung cancer, reflected in a high population-attributable fraction. In many populations, about 85% of lung cancer cases are attributable to cigarette smoking, meaning the vast majority arise because of tobacco exposure. This arises from the strong, dose‑dependent relationship between smoking and lung cancer risk and the fact that carcinogens in cigarette smoke cause genetic mutations in bronchial epithelium. While quitting tobacco reduces risk over time, it does not immediately return to the level of never-smokers, so the fraction remains high but not absolute. The other options are too low or too high to align with the substantial impact of smoking observed in epidemiologic data. Therefore, approximately 85% is the best estimate.