Cigarette Smoke and Lung Cancer: Why Tar Is the Primary Carcinogenic Driver

Cigarette smoke contains >7,000 chemicals; at least 70 are known carcinogens. Tar—the particulate residue—concentrates the most potent DNA-damaging agents.

Key Carcinogens in Tar

Compound	Class	Mechanism
Polycyclic aromatic hydrocarbons (BaP)	Group 1	DNA adducts → TP53 mutations (G→T transversions)
N-nitrosamines (NNK, NNN)	Group 1	Methylate DNA → KRAS activation
Aromatic amines (4-aminobiphenyl)	Group 1	DNA adducts in bladder, lung
Formaldehyde	Group 1	DNA-protein crosslinks
Cadmium, arsenic, chromium, nickel	Group 1	Oxidative stress, repair inhibition

Gas-Phase Contributors

• Carbon monoxide: Carboxyhemoglobin → tissue hypoxia → selects for aggressive clones.
• Hydrogen cyanide: Inhibits cytochrome c oxidase → cellular stress.
• Acrolein: Depletes glutathione, damages TP53.

Synergy

Co-exposure multiplies risk; e.g., PAHs + nicotine-driven proliferation + CO hypoxia = mutagenic milieu. Filter ventilation increases puff volume, depositing tar deeper.

Risk Reduction

• Cessation: risk drops 50% at 10 years, approaches never-smoker at 20–30 years.
• Lung cancer screening (LDCT) for 50–80 pack-year, current/former <15 yr quit.