a. Heredity-only 5–10% of all cancers are attributable to genetics. Hereditary cancers are primarily caused by an inherited genetic defect. Less than 0.3% of the population is carriers of a genetic mutation which has a large effect on cancer risk and this cause less than 3–10% of all cancer.
b. Lifestyle and environment causes---- Cancers are primarily a lifestyle disease with 90–95% of cases attributed to lifestyle and environmental factors. Common lifestyle and environmental factors that contribute to cancer death include:
i. Smoking---The incidence of lung cancer is highly correlated with smoking. Cancer pathogenesis is traceable back to DNA mutations that impact cell growth and metastasis. Substances that cause DNA mutations are known as mutagens, and mutagens that cause cancers are known as carcinogens. Particular substances have been linked to specific types of cancer. Tobacco…Tobacco smoke contains over fifty known carcinogens. Tobacco smoking is associated with many forms of cancer and causes 90% of lung cancer. Tobacco is responsible for about one in three of all cancer deaths in the developed world, and about one in five worldwide
ii. Alcohol…..In Western Europe 10% of cancers in males and 3% of cancers in females are attributed to alcohol. Research has demonstrated the link between tobacco use and cancer in the lung, larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas.
iii. Environmental pollutants ---Cancer related to one's occupation is believed to represent between 2–20% of all cases. Every year, at least 200,000 people die worldwide from cancer related to their workplace. Most cancer deaths caused by occupational risk factors occur in the developed world. It is estimated that approximately 20,000 cancer deaths and 40,000 new cases of cancer each year in the U.S. are attributable to occupation. Millions of workers run the risk of developing cancers such as lung cancer and mesothelioma from inhaling asbestos fibers and tobacco smoke, or leukemia from exposure to benzene at their workplaces.
iv. Diets….. that are low in vegetables, fruits and whole grains, and high in processed or red meats are linked with a number of cancers. A high salt diet is linked to gastric cancer, aflatoxin B1, a frequent food contaminate, with liver cancer, and Betel nut chewing with oral cancer.
v. Lack of exercise--Physical inactivity is believed to contribute to cancer risk not only through its effect on body weight but also through negative effects on immune system and endocrine system.
vi. Obesity--- In the United States excess body weight is associated with the development of many types of cancer and is a factor in 14–20% of all cancer deaths.
vii. Infectious diseases---Worldwide approximately 18% of cancer deaths are related to infectious diseases. This proportion varies in different regions of the world from a high of 25% in Africa to less than 10% in the developed world. Viruses are the usual infectious agents that cause cancer but bacteria and parasites may also have an effect. A virus that can cause cancer is called an oncovirus. (read on the examples of these viruses).
viii. Radiation --Up to 10% of invasive cancers are related to radiation exposure, including both ionizing radiation and non-ionizing radiation. Additionally, the vast majority of non-invasive cancers are non-melanoma skin cancers caused by non-ionizing ultraviolet radiation. Sources of ionizing radiation include medical imaging, and radon gas. Radiation can cause cancer in most parts of the body, in all animals, and at any age, although radiation-induced solid tumors usually take 10–15 years, and can take up to 40 years, to become clinically manifest, and radiation-induced leukemias typically require 2–10 years to appear. Children and adolescents are twice as likely to develop radiation-induced leukemia as adults. Radiation exposure before birth has ten times the effect. Radiation is a more potent source of cancer when it is combined with other cancer-causing agents, such as radon gas exposure plus smoking tobacco.
ix. Physical agents--Some substances cause cancer primarily through their physical, rather than chemical, effects on cells. A prominent example of this is prolonged exposure to asbestos, naturally occurring mineral fibers which are a major cause of mesothelioma, a type of cancer of the serous membrane. Other substances in this category, including both naturally occurring and synthetic asbestos-like fibers such as wollastonite, attapulgite, glass wool, and rock wool, are believed to have similar effects. Nonfibrous particulate materials that cause cancer include powdered metallic cobalt and nickel, and crystalline silica (quartz, cristobalite, and tridymite). Usually, physical carcinogens must get inside the body (such as through inhaling tiny pieces) and require years of exposure to develop cancer.
Titany answered the question on July 27, 2021 at 12:39