Cancer - Causes of Cancer

Agents that cause cancer by disturbing the normal genetic and regulatory processes of cells are called carcinogens.

A cancer-causing gene that induces transformation of normal cells into cancerous cells is called an oncogene.

A normal cellular gene involved in growth and development, which can become an oncogene after mutation or activation, is called a proto-oncogene.

• Chemicals: Nicotine, caffeine, polycyclic hydrocarbons, coal/oil combustion products, and excess sex hormones are carcinogenic (e.g., breast cancer linked to hormones).
• Radiation: X-rays, gamma rays, UV rays, and cosmic rays cause cancer. High UV exposure increases the risk of skin cancer.
• Viruses: Oncogenic viruses carry v-onc genes (e.g., EBV, HPV).
• Oncogenes: Normal cells contain proto-oncogenes (c-onc genes), which, when activated, transform cells into cancerous ones.
• Addiction: Tobacco → mouth, lips, lung cancer; Alcohol → oesophagus, liver cancer; Drugs (marijuana, steroids) → also cause cancer.