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.

A variety of chemicals have been identified as carcinogens.

• Nicotine - present in tobacco products; associated with cancers of the mouth, lips, and lungs.
• Caffeine - identified as a chemical carcinogen.
• Polycyclic aromatic hydrocarbons - produced from the combustion of coal, petroleum, and other organic matter.
• Sex hormones - excess or imbalanced hormonal exposure has been linked with certain cancers, such as breast cancer.

Radiation is a significant physical cause of cancer.

• Ionising radiation: X-rays, gamma rays, and other high-energy radiations can damage DNA and increase the chance of mutation.
• Non-ionising radiation: Excessive ultraviolet (UV) rays from sunlight can damage skin cells and increase the risk of skin cancer.
• Cosmic radiation: Long-term exposure to certain forms of radiation may also contribute to cellular damage.

Certain viruses can transform normal cells into cancerous cells. These are called oncogenic viruses, and they carry specific genes known as viral oncogenes (v-onc).

Examples of oncogenic viruses:

• Epstein–Barr virus (EBV)
• Human Papillomavirus (HPV)

Every normal cell contains genes that regulate growth and development; these are called proto-oncogenes. Proto-oncogenes are normal cellular genes involved in growth regulation.

When a proto-oncogene undergoes mutation or becomes abnormally activated under the influence of carcinogens or other factors, it is converted into an oncogene. An oncogene is a cancer-causing gene that transforms normal cells into neoplastic (cancerous) cells and drives uncontrolled cell division.

Cancer is fundamentally a genomic disease - it arises from damage to DNA, which may be caused by carcinogens generating free radicals or by direct DNA alterations.

Lifestyle habits can increase exposure to carcinogens and raise cancer risk.

• Smoking and tobacco chewing are linked with cancers of the mouth, lips, and lungs.
• Alcohol abuse is associated with cancers affecting organs such as the oesophagus and liver.
• Drug abuse and long-term harmful exposures may further increase risk.

• Carcinogens disrupt normal cellular genetics, potentially transforming growth-regulating proto-oncogenes into cancer-causing oncogenes.
• Chemical factors such as nicotine, polycyclic aromatic hydrocarbons, and imbalanced sex hormones are known to induce various cancers.
• Radiation acts as a physical carcinogen, with ionising (e.g., X-rays) and non-ionising (e.g., UV rays) radiation damaging DNA and increasing cancer risk.
• Biological factors such as oncogenic viruses (e.g., HPV and EBV) carry viral oncogenes that can transform normal cells into cancerous ones.
• Lifestyle habits, particularly smoking, tobacco chewing, and alcohol abuse, significantly heighten the risk for multiple types of cancer.