Cancer Risk Factors
The search for cause(s) of cancer has been going on for centuries. Early researchers said that cancer was a natural result of aging. As cells degenerated, it was believed that some simply became malignant. Others said cancer was hereditary, and investigations into genetics began. Then some began to consider chemical links while still others questioned whether viruses or bacteria were at fault. Finally, the "irritation" theory became popular,and researchers began trying to identify irritants — such as tobacco and coal tar — that would cause cancer in laboratory animals. Ultimately, though, cancer experts were forced to confront the fact that although all these factors might be involved, none of them invariably cause cancer. Not every animal or person exposed to an irritant or a particular chemical in the laboratory developed cancer, nor did all elderly people or everyone with a family history of cancer get it. As a result, scientists had to abandon the theory that cancer had a single cause.
However, despite the fact that there is yet no absolute agreement among the cancer research community in terms of what actually causes cancer, scientists are certain that many factors can be linked to cancer. These factors, including many other possible causes of cancer suggested by cancer researchers, are believed to be "cancer risk factors." These risk factors include eating habits, lifestyle, living or working environments, genetics, and many others. Following are some major cancer risk factors identified by researchers with the support of scientific statistics:
Cigarette smoking alone is directly related to at least one-third of all cancer deaths annually in the United States. Cigarette smoking is the most significant cause of lung cancer and the leading cause of lung cancer death in both men and women. Smoking is also responsible for most cancers of the larynx, oral cavity, and esophagus. In addition, it is highly associated with the development of, and deaths from, bladder, kidney, pancreatic, and cervical cancers. Tobacco smoke contains thousands of chemical agents, including 60 substances that are known to cause cancer (carcinogens).
The health risks with cigarette smoking are not limited to smokers. Exposure to environmental tobacco smoke significantly increases a nonsmoker's risk of developing lung cancer. Environmental tobacco smoke is the smoke that nonsmokers are exposed to when they share air space with someone who is smoking.
The lifestyle factor that has received the most attention in recent years is diet. Evidence suggests that about one-third of the cancer deaths each year that occur in the United States are related to dietary factors. These include types of food, preparation methods, portion size, variety, and overall caloric balance.
A high-fat diet has been associated with an increased risk for cancer of the prostate, endometrium, and colon and rectum. It is believed that a high-fat diet is a cancer promoter, with numerous theories to explain the effects of excess fat. For instance, excess fat seems to be involved in the production of free radicals, which play a role in many types of cancer. A high-fat diet also increases the flow of bile acids into the intestine, which can promote colon cancer.
Study results suggest that certain food additives, as well as preparation methods, can either cause or promote cancer. Even some so-called natural methods of preserving foods are not considered safe. For example, pickled, cured, and smoked products appear to promote stomach cancer, possibly due to nitrites used in curing as well as to other compounds produced during smoking and pickling. The decrease in gastric cancer incidence is largely due to modern refrigeration and a reduction in pickled, cured, and smoked food products.
By definition, cancer is really a disease of genes. Genes are very small molecules in our cells, which determine almost everything in our body. Genes that control the genetics and heredity of each cell are strung like beads on a necklace along the cell's DNA in the cell nucleus. In a benign or malignant tumor, several of the genes regulating these processes are abnormal (mutated). Abnormal genes may be inherited or damaged by carcinogens, viruses, errors in cell division, and as yet unknown factors.
A number of the most common cancers, including breast, colon, ovarian, and uterine cancer, recur generation after generation in some families. In addition, certain genetic factors may predispose those affected to specific cancers. A few rare cancers, such as the eye cancer, retinoblastoma, and a type of colon cancer, have been linked to specific genes that can be tracked within a family.
Although it is helpful to know the role that our genetic heritage may play as a possible cause of cancer, scientists believe that environmental influences and our behaviors may outweigh the risks inherent in our family tree.
Occupation and Environment
Scientists have long been aware of the linkage between one's health conditions and one's occupation and environment.
People who have direct contact to carcinogenic agents in the workplace are at the highest risk for developing cancer. For example, a recent study suggests that people with brain cancer are more likely to have worked in certain occupations than similarly aged people without brain cancer. Many cancer-causing chemicals have been identified and many of them are banned from manufacture in the United States.
More recently, investigators have identified a link between the environment and skin cancer. The environmental factor is something we depend on for our life: sunlight. Scientists have found that ultraviolet light causes mutations of genes, producing a carcinogenic effect. Now, we not only know that tumors may appear years after the damaging effects of sunlight, but also the risks from exposure to ultraviolet light are greater for light-skinned people. Statistics show that in the U.S. alone about a million new cases of skin cancer (basal and squamous cell carcinomas) occur annually, rivaling the incidence of all other types of cancer combined.
Because viruses can invade and alter cells' genetic material, viral infections are implicated in some cancers. The Epstein-Barr virus, for example, is associated with Burkitt lymphoma, a tumor found mainly among children in Africa. The hepatitis B virus is responsible for much of the liver cancer around the world. The highest rates of hepatitis B infection in the world is in China, Taiwan, Japan, and Thailand with equally high rates of liver cancer in these countries. The human papilloma virus that causes genital warts has been shown to play an important causative role in cervical cancer. The human T-cell leukemia virus, a close relative of the virus that causes acquired immunodeficiency syndrome (AIDS), is associated with a cancer known as Kaposisarcoma and some types of Non-Hodgkin lymphomas.
Cancer risk factors are not limited to those listed above. There are still other risk factors such as ethanol use, use of certain medications, hormones, and reproductive and sexual behavior. With further scientific research, more cancer risk factors will be identified in the future.
In summary, cancer is caused by both external (chemical, radiation, and viruses) and internal (hormones, immune conditions, and inherited mutations) factors. Causal factors may act together, or in sequence, to initiate or promote carcinogenesis.