Causes of Cancer

Age. Cancer can manifest at any age, it does not exclusively affect adults. In general, cancer often requires years to develop and therefore most people diagnosed with cancer are 65 or older. Consequently, age is a very significant risk factor for cancer.

Infections. Certain bacteria can cause or increase the risk of cancer because of their capacity to interrupt the signals that control cell growth and proliferation, to weaken the immune system or to induce chronic inflammation.

Notable infections include: Hepatitis B and C virus infections, which are associated with the onset of hepatic cancer. Human papillomavirus infection (HPV), associated with an increased risk of cervical, vulvar, vaginal, penile, anal canal, mouth and throat cancers. The Epstein–Barr virus, which is linked to nasopharyngeal carcinoma and Burkitt’s lymphoma. Human immunodeficiency virus (HIV) is associated with Kaposi sarcoma and non-Hodgkin’s lymphomas. The bacteria Helicobacter pylori show a correlation with an increased risk of developing stomach cancer. Infections due to parasites such as Schistosoma haematobium have been linked to a greater risk of bladder cancer; Opisthorchis viverrini infection is related to a higher incidence of hepatic cancer.

Hormones. Both female and male hormones, while they are essential for certain physiological functions, play a key role in three very common cancers: breast cancer, ovarian cancer and prostate cancer. These biochemical substances can stimulate the appearance of tumours in hormone-sensitive tissues and accelerate the progression of the disease or contribute to its recurrence after the tumour has entered into remission.

Chronic inflammation. Inflammation is the body’s response to an attack, whether it is an infection, a wound or the action of a toxic agent. In the case of chronic inflammation, the inflammatory process may start even when there is no damage and may not finish when it should. Chronic inflammation may be due to infections that do not disappear, abnormal immune reactions or conditions such as obesity. Chronic inflammation can eventually cause damage to DNA and produce cancer. People with a chronic inflammatory bowel disease such as ulcerative colitis or Crohn’s disease have a greater risk of developing colon cancer.

Immunosuppression. Some medications, immune system disorders and certain infections (e.g., HIV) reduce the immune system’s ability to detect and destroy cancer cells or fight against cancer-causing infections.

Radiation. Radiation at certain wavelengths, called ionising radiation, has enough energy to damage DNA and cause cancer. Different types of ionising radiation include ultraviolet (UV), radon, X-ray and other forms of high-energy radiation. Non-ionising, low-energy forms of radiation, such as visible light, radiofrequency waves from mobile phones or magnetic fields, do not damage DNA and there is no evidence they cause cancer.

Substances in the environment. Certain industrial, household or workplace chemicals have been related to cancer. Air pollution is associated with lung, kidney, bladder and colorectal cancers.

Family history. Only a small portion of cancer cases are due to an inherited disorder. If cancer is prevalent in a given family, there may well be mutations that are passed from one generation to the next. The need for genetic studies to determine the presence of inherited mutations that increase the risk of presenting certain kinds of cancer should be assessed on an individual basis.