With the possible exception of AIDS, there is probably no disease that strikes more fear in people than cancer. The term cancer refers to a group of diseases characterized by uncontrolled disorderly cell growth. It is the second leading cause of death, accounting for 20% of all deaths. It is the leading cause of death among adults ages 25 through 64. Cancer deaths have risen 7% in the last 20 years. (Heart disease deaths, the number one cause of deaths, by comparison have fallen 50% during the same time period.) The major cause of the increase in cancer deaths is lung cancer. If lung cancer deaths were excluded, cancer deaths would have declined 14% between 1950 and 1990. Death rates for many major cancer sites have leveled off or declined over the past 50 years. Still, 42% of Americans will eventually develop one or more of the 100 different forms of cancer; 40% of people who get cancer will be alive 5 years after diagnosis. Most of this 40% can be considered cured, whereas others still have evidence of cancer. Cured means that a patient has no evidence of disease and has the same life expectancy as a person who never had cancer. Although it strikes more frequently with advancing age, cancer causes the death of more children than any other disease. The chances of developing cancer can be reduced by assuming control of the things you do every day .Cell growth is controlled by deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in the nucleus of each cell in the body. If the nuclei lose the ability to regulate and control this growth, cellular metabolism and reproduction are disrupted and a mutant cell is produced that has a variation in form, quality, and function from the original. When a mass of these cells develops, it is a neoplasm, or tumor. It may be malignant (cancerous) or benign (non cancerous). A benign tumor will not spread throughout the body. It is enclosed by a membrane that prevents it from invading other tissues. A benign tumor is not life threatening unless it is in an area that interferes with normal functioning. A malignant tumor is the most dangerous tumor because it has a tendency to spread from its original location to other parts of the body, which can make it life threatening. Cancer cells can crowd out normal cells, invade surrounding tissue, and move through the lymphatic or circulatory system to infiltrate other areas of the body. (The lymphatic system is a network of nodes and vessels that serves to drain fluid from tissues and return it to the bloodstream. It is also part of the body’s immune system.) The process by which cancerous cells spread from their original site (primary site) to another location (secondary site) is called metastasis. This ability of cancerous cells to metastasize makes early detection critical.
Causes
Cancer is caused by both external (chemicals, diet, radiation, viruses, pollutants, etc.) and internal (hormones, immune conditioning, and inherited mutations) factors. Any combination of these factors may work together to initiate or promote carcinogenesis-the development of cancer cells. Ten or more years often pass between exposures or mutations and the actual detection of cancer.
Although the causes of cancer are not clearly understood, correlations have been found linking cancer to everything from genetic factors to exposure to the sun’s radiation. Many carcinogens (cancer causing agents) trigger development of cancer.
An inherited tendency for cancer has been theorized for years. Everyone seems to have genes that may cause cancer, but not everyone gets cancer. In most cases environmental factors actually activate the cancer. A good example of the interplay between genetic and environmental factors is cigarette smoking. Approximately 87% of lung cancers occur in cigarette smokers, but only 15 % of smokers develop lung cancer. Why not the other 85%? The 15% who develop cancer are thought to be susceptible to the disease on the basis of their genes. If they had not activated the cancer genes by smoking, they probably would not have contracted the disease.
A gene that causes cancer is called an oncogene. Within a tiny segment of DNA is an area that can be activated to form an oncogene. This segment is called a protooncogene, and unless it is activated, it will never become an oncogene or cause cancer. If an oncogene is formed, it acts with other oncogenes to produce abnormal cells that can replicate and spread. The presence of certain oncogenes is being used to predict which tumors are likely to recur after surgery and/or to identify family members at risk. Suppressor genes also playa role in cancer. Suppressor genes exist in normal cells and control cell growth. If suppressor genes mutate, cells are permitted to grow unrestrained.
Another explanation of cancer is an error in cell duplication on the basis of chance alone. Several trilion new cells are formed each year, and perfect duplication does not occur with each new cell formation. When an abnormal cell develops, the immune system recognizes it as a rogue cell and attacks it. Every cancer cell needs to be killed because almost all cancers arise from a single cancer cell. Cancer develops as a result of the immune system’s failure to clear the body of cancer cells. This is one reason the immune system is receiving considerable attention among cancer researchers.
Much research appears to link psychological states with the prevalence of disease in individuals. People with positive, involved attitudes who view life’s challenges as opportunities for personal growth seem to have fewer diseases and recover from them more often. Individuals who feel lonely and depressed and lack appropriate social support are more cancer prone than their mentally healthy counterparts.
Emotional factors, such as stress reduction, social support, and the ability to express and cope with the range of emotions brought on by a frightening diagnosis of cancer, have been linked to the progression of cancer. Several studies have reported that patients who participate in support groups while receiving standard medical care live significantly longer than those receiving medical care alone. Conversely, cancer patients who are socially isolated have poorer survival rates than those with more social connections. This doesn’t suggest that stress and social isolation cause cancer. It does suggest a significant correlation between emotion and the progression of cancer once the disease is established. Many experts believe that a person’s emotional state somehow bolsters the body’s natural cancer-fighting power.
Although some of these concepts are controversial, it is generally accepted that substances such as tobacco, tobacco smoke, alcohol, asbestos, herbicides, and pesticides are carcinogens. Scientists believe more than 80% of all cancers are associated with lifestyle factors that are easily controlled-diet, smoking, and exposure to the sun. Almost two thirds of cancer deaths are attributed to diet and tobacco. According to a 20-year study of 115,195 healthy women ages 30 to 55, one third of cancer deaths are caused by excessive weight.
One of the major carcinogens may be radiation from the sun, more specifically excessive exposure to the ultraviolet (UV) rays of the sun. People who spend hours in the sun without protection have an increased risk for skin cancers. UV light peaks from 10 AM to 2 PM (11 AM to 3 PM during daylight savings time). Avoiding sun exposure during these hours can cut UV-light exposure up to 60%. Fortunately, most major newspapers now include the UV index as a routine part of the weather report . The index is based on a 15-point scale with 15 representing the highest exposure to UV light. Sunscreen lotions absorb or block UV rays and therefore protect against skin cancer. For most people in the United States sunscreen with a sun protection factor (SPF) of 15 is usually sufficient. Using tanning beds also increases the risk for skin cancer.
Finally the herpes viruses have been connected with cancer of the cervix. Viruses may be involved in the development of some forms of leukemia, Hodgkin’s disease, and Burkett’s lymphoma. The exact role of viruses in causing cancer is not known, but they may provide an opportunistic environment for cancer development. Other researchers have suggested that a combination of factors, of which the virus may play a part, rather than the virus itself causes a cancer.
Sites
The American Cancer Society reports each year on the incidence and number of deaths from cancer for a variety of sites. Skin cancer is the most common cancer. More than 800,000 people are diagnosed annually with basal and squamous cell skin cancer. Almost all of these are considered sunrelated cases. Fortunately, the majority of skin cancers are highly curable. For both genders the cancer that kills most often is lung cancer. Excluding basal cell and squamous cell carcinomas, the breasts are the most prevalent cancer site for women and the prostate is the leading cancer site for men. In 1995 an estimated 244,000 new cases of prostate cancer and 182,000 new cases of breast cancer were reported. For any cancer, early detection is imperative. If cancer is diagnosed while it is still localized, the cure and/or survival rate may be 90% or higher for some cancers such as skin, colon, and rectum cancers.
Treatment
Cancer is often treated surgically. A surgeon removes the malignant tissue and some additional normal tissue. Today, the tendency is to remove less surrounding normal tissue and combine surgery with chemotherapy and/or radiotherapy. Radiotherapy is the use of radiation to destroy cancer cells or their reproductive mechanism so that they cannot replicate. This treatment can cause unpleasant side effects, such as diarrhea, itching, and difficulty in swallowing. When cancer has spread throughout the body, chemotherapy is used. Chemotherapy is the use of drugs and hormones to treat cancers such as acute leukemia and testicular cancer. About 50 anticancer drugs are in use.
Another technique that offers hope for treating cancer is immunotherapy. This process involves stimulating the body’s immune system to help destroy malignant growths. Interferon and interleukin-2 (proteins produced by the body to protect against viral invasions of healthy cells) are undergoing research for this purpose. Interferon is used for treatment of a rare blood cancer called hairy cell leukemia. Interleukin-2 is under study in the treatment of kidney cancer and melanoma. Vaccines against several types of cancer are also being developed.
New technologies enhance the diagnosis and treatment of cancer. Magnetic resonance imaging (MRI) and computerized tomography (CT scanning) help to detect and map hidden tumors. Bone marrow transplantation is now a treatment option for select patients with leukemia and lymphoma. And, novel drug-delivery systems are allowing more drugs to reach cancer cells.
Psychosocial and behavioral research is also having a significant impact on symptoms of cancer and its treatment, such as pain, nausea, and vomiting. Interest in this area of research has been sparked by the mounting evidence that lifestyle and environmental factors influence a person’s general health and chances of developing cancer, as well as the mental and emotional ability to cope with cancer if it occurs.
Exercise
Researchers are currently investigating the role of exercise in the prevention of some types of cancer, including colon cancer, breast cancer, and cancer of the reproductive organs. Since 1980 at least eight studies involving large numbers of people in America, Europe, and China have examined the relationship between physical activity and colon cancer; seven concluded that exercise reduces risk. A more recent study of 17,607 college graduates ages 30 to 79 years also confirmed a lower risk of colon cancer and lung cancer among men who were physically active. Other studies involving the risk of breast cancer among more than 5000 alumnae of 10 colleges and universities revealed 86% higher rates for nonathletes compared with their athletic peers. In another study of 25,000 women in Washington state, women who worked at physically demanding jobs were less likely to have breast cancer than those with sedentary jobs. Cancers of the female reproductive system also seem to be related to exercise. In the Harvard alumnae study, women who played sports during their college years were less likely to develop cervical, uterine, ovarian, or breast cancer than nonathletes .
How Much Exercise is Enough?
If the results of colon cancer studies are representative of other cancers, exercise that requires as little as 1000 calories per week lowers the risk of cancer. Although large-scale studies indicate that physical fitness appears to postpone the risks of dying from a variety of malignancies, the evidence falls short of cause and effect. Several hypotheses attempt co explain the reasons exercise may prevent cancer. One possible mechanism involves the effect of exercise in reducing body fat. The amount of body fat is positively correlated with the incidence of cancer. In the case of colon cancer, physical activity promotes bowel movements, thus reducing the exposure of the intestinal wall to potentially toxic fecal material. some studies have also indicated that exercise may augment or stimulate the body’s immune system in several ways, the end result being that cancerous cel1s are recognized and destroyed early in their development.
