Written By: Dr. Vishal Saxena
Cancer is the abnormal, uncontrolled growth of cells in our body that involves multiple disorders. According to the American Cancer Society, deaths arising from cancer constitute 6-10% of the annual deaths recorded worldwide and kill more than 3500 million people annually all over the world. Several risk factors are implicated in the causation of cancer, as discussed here.
Advancing age is the most important risk factor for cancer overall, and for many individual cancer types. In the United States, more than 50% of cancers occur in people older than 65. One-quarter of new cancer cases are diagnosed in people aged 65 to 74. The median age at diagnosis is 61 years for breast cancer, 68 years for colorectal cancer, 70 years for lung cancer, and 66 years for prostate cancer. Bone cancers and leukemia’s are most frequently diagnosed among people under age 20.
- Family History
Some families have a significantly higher risk of developing certain cancers such as breast, colon, brain and ovarian cancer.
- Genetic Predisposition
- Inherited Cancer Syndromes
|Rb||Childhood eye cancer, Bone and Breast cancer|
|P53||Lung, Colon, Breast, and Brain cancers, Li Fraumeni syndrome (a multi-cancer syndrome)|
|APC||Familial adenomatous polyposis/colorectal cancer|
|NF-1,NF-2||Neurofibromatosis 1 & 2|
|BRCA-1,BRCA-2||Breast and ovarian cancers|
|MEN-1, RET||Multiple endocrine neoplasia I; IIa; IIb|
- Inherited Syndromes of Defective DNA Repair Genes
Xeroderma pigmentosum can lead to skin cancers; Ataxia telangiectasia can lead to lymphoma, leukemia, and brain tumors; and Bloom’s syndrome, and Fanconi’s Anemia can lead to leukemia.
Japanese have extremely high rates of stomach cancer. Nasopharyngeal carcinoma is more common in African children and South Eastern China adults. Liver cancer is more common in Southeast Asia. Burkitt lymphoma and Kaposi sarcoma is more common in Africa.
Tobacco smoking causes cancer of lung, larynx (voice box), oral cavity (mouth), esophagus, pharynx (throat), bladder, kidney, liver, stomach, pancreas, colon, rectum, and cervix, and leukemia. Tobacco chewing causes cancers of the mouth, esophagus, and pancreas.
Drinking alcohol can increase your risk of cancer of the oral cavity (mouth), pharynx (throat), larynx (voice box), esophagus, liver, breast, colon, and rectum.
- Cancer causing agents
- Aflatoxins: toxins found on agricultural crops such as maize (corn), and peanuts. Exposure is associated with an increased risk of liver cancer.
- Arsenic: by smoking tobacco, and drinking contaminated water, exposure is associated with an increased risk of bladder, skin, lung, liver, kidney, and lymphatic and hematopoietic cancer.
- Vinyl chloride: by inhaling contaminated air or tobacco smoke; exposure is associated with an increased risk of liver, brain, lung cancers, lymphoma and leukemia.
- Thorium: used in lantern mantles and in welding rods, dust exposure increases the risk of lungand pancreatic
- Asbestos: used in insulation, fireproofing materials, and automotive brakes, exposure is associated with an increased risk of lung cancer and pleural mesothelioma (cancer of lung lining).
- Coal Tar: produced in foundries, and also used in pavement tar, coal-tar paints, and skin disorders medications, exposure increases the risk of skin, lung, bladder, kidney, and intestinal cancers.
- Soot: a byproduct of the incomplete burning of wood, plastics, and household refuse, exposure leads to scrotal, skin, lung, esophageal, and lung cancers.
Exposure to ultraviolet (UV) radiation by sun, sunlamps, and tanning booths can lead to skin cancer. People of all ages and skin tones should limit the amount of time they spend in the sun, especially between 10:00 AM and 4:00 PM.
Higher-energy, ionizing radiation like radon, x-rays, gamma rays, alpha particles, beta particles, and neutrons cause cancers like leukemia and sarcomas. Leukemia incidence is increased in atomic bomb victims. Thyroid cancer incidence is increased in head and neck radiation.
Obesity may have an increased risk of cancers of the breast, colon, rectum, endometrium (lining of the uterus), esophagus, kidney, pancreas, and gallbladder, and possibly prostate cancer.
Taking combined menopausal hormone therapy (estrogen plus progestin, which is a synthetic version of progesterone) can increase risk of breast cancer. Menopausal hormone therapy with estrogen alone increases the risk of endometrial cancer.
- Chronic inflammation
Chronic inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease have an increased risk of colon cancer.
Tamoxifen, a drug used to treat breast cancer, increases the risk of endometrial cancer. Long-term use of androgens may slightly increase the risk of liver cancer. Treatment of cancer with certain chemotherapy drugs (alkylating agents) may increase the risk of developing a second cancer, years later.
The common cancers among transplant recipients are non-Hodgkin lymphoma (NHL) and cancers of the lung, kidney, and liver.
- Infectious agents
- Epstein – Barr virus (EBV): Infection is most commonly transmitted by contact with saliva, such as through kissing or by sharing toothbrushes or drinking glasses. It can cause lymphomas and cancers of the nose and throat.
- Hepatitis B Virus and Hepatitis C Virus (HBV and HCV): Infection can be transmitted via blood (for example, by sharing needles or through blood transfusions), sexual contact and from mother to baby at birth. Chronic infections with HBV or HCV can cause liver cancer.
- Human Immunodeficiency Virus (HIV):
Infection can be transmitted via blood and through sexual contact. Infection with HIV increases risks of Kaposi sarcoma (a skin cancer), lymphomas, and cancers of the cervix, anus, lung, liver, and throat.
- Human Papillomaviruses (HPVs): Infection spreads through direct sexual contact. Infection with HPVs cause nearly all cervical cancers, most anal cancers and many oropharyngeal, vaginal, vulvar, and penile cancers.
- Human T-Cell Leukemia/Lymphoma Virus Type 1 (HTLV-1): Infection spreads via blood (by sharing needles or through transfusions), through sexual contact, and from mother to child in the womb or via breastfeeding. It can cause leukemia and lymphoma.
- Kaposi Sarcoma-Associated Herpes virus (KSHV): Infection most commonly spreads through saliva. It can cause Kaposi sarcoma (a skin cancer) in AIDS patients.
- Helicobacter pylori (H. pylori): Infection is spreads through consumption of contaminated food or water. It can cause gastric cancer, and lymphoma.