Carcinogens and DNA Damage: How Cancer Develops

Carcinogens are agents that cause cancer by damaging DNA, the genetic blueprint for proteins. When DNA is altered, cells may proliferate uncontrollably, forming tumors—benign or malignant.

Major Classes of Carcinogens

• Chemical: Tobacco smoke (PAHs, nitrosamines), asbestos, benzene, aflatoxins, arsenic, certain industrial chemicals.
• Physical: UV radiation (sun, tanning beds), ionizing radiation (X-rays, radon, nuclear).
• Biological: HPV (cervical, oropharyngeal cancer), HBV/HCV (liver cancer), H. pylori (stomach cancer), EBV (lymphomas).

Mechanisms of DNA Damage

• Adduct formation: Covalent binding to DNA bases (e.g., benzo[a]pyrene from smoke).
• Oxidative stress: Reactive oxygen species (ROS) damage bases, cause strand breaks.
• Cross-linking: Agent links DNA strands or DNA-protein, blocking replication.
• Epigenetic alteration: Methylation changes silencing tumor suppressors.

Risk Modifiers

• Dose, duration, route of exposure.
• Genetic susceptibility (DNA repair capacity, metabolic enzyme variants).
• Co-exposures (e.g., smoking + asbestos = synergistic lung cancer risk).

Reducing Exposure

• Avoid tobacco; test home for radon.
• Use sunscreen, limit midday sun.
• Get HPV and HBV vaccines.
• Follow workplace safety protocols for chemicals.
• Eat antioxidant-rich diet (fruits, vegetables).

Carcinogenesis is multistep; reducing exposure at any stage lowers lifetime risk.