Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread (malignant) to other parts of the body. These contrast with benign tumors, which do not spread.
The development of a cancerous tumour in otherwise healthy tissue is the result of a complex series of events beginning with a single cell that has acquired malignant properties as a result of changes in a cell’s DNA – its genetic “blueprint.” The DNA changes may be inherited from our parents or caused, directly or indirectly, by carcinogens (Substances whose exposure can lead to cancer).
Before malignant cells can cause symptoms or be detected, successive generations of daughter cells must divide to form a tumour measuring about one cubic centimeter, weigh about one gram and comprise one billion cells.
Of importance, however, is preventing the development of cancerous cells through adoption of healthy lifestyles, avoiding exposure to known cancer-causing substances, and taking medicines or vaccines that can prevent cancer from developing. With cancer, prevention is the most cost-effective long-term strategy for the control of cancer.
Diet and physical exercise
Epidemiological studies indicate that diets such as red meat and processed meat- any meat which has been modified either to improve its taste or to extend its shelf life-increases the risk for some cancers. Additionally, deficiency of micronutrients such as vitamins B12, folic acid, B6, niacin, C, or E, or iron, or zinc, appears to mimic radiation in damaging DNA which has been associated with cancer development.
Dietary modification is an important approach to cancer control. Diets high in fruits and vegetables (more than 500 grams per day) may have an independent protective effect against many cancers; apparently raw vegetables provide the largest health benefits. This positive effect of fruits and vegetable consumption is probably due to their high antioxidant content, which mitigates the oxidative damage to DNA by carcinogens.
Furthermore, epidemiological investigations show that the greater effects in cancer risk reduction due to fruit and vegetable consumption is observed in people with bad habits such as alcohol use, obese and smoking. Such populations should be encouraged to take the recommended amounts of fruits and vegetables servings.
Currently, there is irrefutable evidence indicates that regular physical activity and the maintenance of a healthy body weight, along with a healthy diet, considerably reduce cancer risk.
Alcohol and alcoholic beverages
Drinking alcohol raises the risk of some cancers. Drinking any kind of alcohol can contribute to cancers of the mouth and throat, larynx (voice box), esophagus, colon and rectum, liver, and breast (in women). The less alcohol you drink, the lower the risk of cancer.
Cigarette smoking and other forms of tobacco use including chewing and snuff, causes many types of cancer, including cancers of the lung, oesophagus, larynx (voice box), mouth, throat, kidney, bladder, pancreas, stomach and cervix.
Second-hand smoke too, has also been proven to cause lung cancer in non-smoking adults.
Furthermore, tobacco use in addition to heavy drinking of alcohol substantially increases the risks of cancer.
In low-income countries, the leading causes of tobacco deaths are cardiovascular diseases, chronic obstructive pulmonary disease, other respiratory disease (chiefly tuberculosis) and lung cancer. Therefore, interventions to reduce tobacco use will have much broader benefits than just in terms of cancer risk reduction.
In 2012, approximately 15% of all cancers were attributable to infectious agents such as aflatoxicosis, helicobacter pylori (common in peptic ulcer patients), human papilloma virus (HPV), hepatitis B and C, and Epstein-Barr virus, malaria and Human immunodeficiency virus type 1 (HIV-1).
Development of effective treatments and controls for these infections will help reverse cancer incidents. Vaccines are available for malaria, hepatitis B virus and some types of HPV and can reduce the risk of for infection-attributable cancers.
Pollution of the environment (air, water and soil) with carcinogenic chemicals (cancer-causing agents) contributes to the cancer burden in human populations.
Heavy metals have been found in toxic quantities in drinking water due to widespread pollution of rivers and wells. Almost all heavy metals including Arsenic, cadmium, chromium, and nickel are known carcinogens.
Occupational exposure such as wood dust (sawmills and carpentry industries) and welding fumes are known to cause eye, lung and other cancers.
International Agency for Research on Cancer (IARC) has determined that there is enough evidence to say that outdoor air pollution can cause cancer in people.
Policies and regulations should be in put in place or enforced to counter wanton waste and environmental pollution and protect public health.
Exposure to all types of ionizing radiation (e.g. x-rays/gamma rays), from both natural and man-made sources, increases the risk of various types of malignancy including leukemia and a number of solid tumours.
Risks increase when the exposure occurs at a young age and also when amount is higher.
Ultraviolet (UV) radiation, and in particular solar radiation, is carcinogenic to humans, causing all major types of skin cancer. Although it’s not practical (or advisable) to completely avoid solar radiation, avoiding intense exposure, use of sunscreen and protective clothing are effective preventive measures.
Breast-feeding reduces the risk for estrogen receptor-negative and progesterone receptor-negative breast cancer (some aggressive and difficult-to-treat breast cancers that disproportionately affect African American women), according to a study conducted at Columbia University’s Mailman School of Public Health in 2012.
The study also indicated that having three or more children without breast-feeding was associated with an increased risk for estrogen receptor-negative and progesterone receptor-negative breast cancer. Therefore, multiparous women (given birth more than once) should be encouraged to breastfeed their infants.
IARC, an affiliate of WHO, conducts both epidemiological and laboratory research into the causes of human cancer and publishes its findings, including the detailed evidence to support them, in volumes known as monographs. For a more comprehensive list of cancer- causing agents visit their webpage at https://monographs.iarc.fr/agents-classified-by-the-iarc/.