Causative factors

• Exposure to chemical carcinogens (chemicals that cause cancer)

  • e.g. ethidium bromide, benzo(a)pyrene in cigarette smoke, sodium nitrite in preserved food
• Exposure to excessive ionizing radiation and UV radiation

  • e.g. Ionizing radiation -> cosmic radiation (from outer space), radioactive fallout, radon gas, x-rays, gamma-rays, UV radiation -> from the sun
• Agents that cause inflammation -> generates DNA-damaging oxidizing agents in the cell
• Infection by certain viruses and bacteria

  • Hepatitis B and C -> liver cancer
  • Human papillomavirus (HPV) -> cervical cancer
  • Human immunodeficiency virus (HIV) -> causes AIDS -> greater risk of lymphoma and Kaposi sarcoma (rare)
  • Epstein barr virus -> Burkitt's lymphoma and nasopharyngeal carcinoma
  • Helicobacter pyloris -> stomach cancer and lymphoma
• How does viruses promote cancer development?

  by integrating viral DNA or viral oncogene into DNA of infected cells -> insertion of viral DNA may disrupt a TS gene or convert a proto-oncogene to a n oncogene