Cancer is caused by genetic changes that cause uncontrolled cell growth and tumour formation.
Sporadic cancers are caused by DNA damage and genomic instability, while a minority are caused by inherited genetic mutations. Most cancers are related to environmental, lifestyle, or behavioural exposures. Cancer is generally not contagious, but can be caused by on co viruses and cancer bacteria. The environmental environment encompasses not only biophysical factors but also lifestyle and behavioural factors.
Over one third of cancer deaths worldwide can be avoided by reducing exposure to known factors. Common environmental factors include exposure to chemical and physical agents, environmental pollutants, diet and obesity, infections, and radiation. These factors alter the function of genes within cells, and many genetic changes are required before cancer develops. Ageing is also an important aspect to consider when evaluating risk factors for cancer development, as many molecular and cellular changes accumulate during ageing and eventually manifest as cancer. Some of the key factors include :
Genetics
Over 50 hereditary forms of cancer exist, but less than 0.3% of the population are carriers of a cancer-related genetic mutation, accounting for 3-10% of all cancer cases. The majority of cancers are non-hereditary, or sporadic cancers. Hereditary cancers are primarily caused by inherited genetic defects. 11 syndromes are genetic disorders where inherited genetic mutations in one or more genes predispose individuals to the development of cancers and may cause early onset. The risk of cancer in these syndromes varies, with some diseases not being the primary feature and being a rare consequence.
Physical and chemical agents
Carcinogens, such as inhaled asbestos, dioxins, and tobacco smoke, are linked to specific types of cancer. Approximately 20,000 cancer deaths and 40,000 new cases of cancer are attributable to occupation in the U.S., with at least 200,000 people dying worldwide from workplace-related cancers. Millions of workers are at risk of developing cancers like lung cancer and mesothelioma from inhaling asbestos fibres and tobacco smoke, or leukaemia from exposure to benzene. Cancer related to one’s occupation accounts for 2-20% of all cases. Most cancer deaths caused by occupational risk factors occur in the developed world. Job stress is not a significant factor in lung, colorectal, breast, and prostate cancers. Exposure to the chemical 2,4-D, which is combined with another pesticide or herbicide, Agent Orange, at a 50:50 ratio, increases the risk of non-Hodgkins lymphoma.
Alcohol
Chronic damage due to alcohol consumption can lead to liver cirrhosis and the development of hepatocellular carcinoma, a form of liver cancer.
Alcohol is an example of a chemical carcinogen. The World Health Organisation has classified alcohol as a Group 1 carcinogen.In Western Europe 10% of cancers in males and 3% of cancers in females are attributed to alcohol. Worldwide, 3.6% of all cancer cases and 3.5% of cancer deaths are attributable to alcohol. In particular, alcohol use has been shown to increase the risk of developing cancers of the mouth, oesophagus, pharynx, larynx, stomach, liver, ovaries, and colon.
Diet
Some specific foods have been linked to specific cancers. Studies have shown that individuals that eat red or processed meat have a higher risk of developing breast cancer, prostate cancer, and pancreatic cancer. This may be partially explained by the presence of carcinogens in food cooked at high temperatures. Several risk factors for the development of colorectal cancer include high intake of fat, alcohol, red and processed meats, obesity, and lack of physical exercise. A high-salt diet is linked to gastric cancer. Aflatoxin B1, a frequent food contaminate, is associated with liver cancer. Betel nut chewing has been shown to cause oral cancers.
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. Every year, nearly 85,000 new cancer diagnoses in the United States are related to obesity. Individuals who underwent bariatric surgery for weight loss have reduced cancer incidence and mortality.
Hormones
Some hormones play a role in the development of cancer by promoting cell proliferation. Insulin-like growth factors and their binding proteins play a key role in cancer cell growth, differentiation and apoptosis, suggesting possible involvement in carcinogenesis.Macroscopic appearance of invasive ductal carcinoma of the breast. The tumor is the pale, crab-shaped mass at the center, surrounded by normal, yellow fatty tissue.
