Cancer is a group of many related diseases in which abnormal cells grow out of control and spread.
KEYWORDS
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Carcinogens
Carcinoma
Metastasis
Oncogenes
Oncology
Osteosarcoma
An Ancient Affliction
The disease we call cancer has been around as long as we have. Evidence of cancerous growths, or tumors, has been found among fossilized bones and in human mummies dating from ancient Egypt. The ancient Greek physician Hippocrates (hi-POK-ra-tees) was the first to use the word "carcinoma" (kar-si-NO-ma) to describe various kinds of tumors. Hippocrates noted that parts sticking out from some tumors looked like the limbs of a crab. The word "cancer" comes from the Latin word for crab. In 1913, only one in nine people had a chance of being alive five years after a diagnosis of cancer. Today, depending on the cancer, more than 50 percent of people with cancer will survive the disease. For many types of cancer, early detection and treatment result in a normal lifespan.
What Is Cancer?
In all forms of cancer, cells grow out of control and may spread. In the United States, half of all men and one third of all women will develop one type of cancer or another during their lifetime. Almost everyone knows someone who has had cancer, and it is natural for children to worry that they might get it. But cancer in children is very rare. Some cancers are more common than others. The cancers that adults get most frequently are cancers of the skin, lungs, and colon and rectum. Breast cancer is a common cancer among women. Childhood cancers include leukemia (loo-KEE-mee-ya), lymphoma (lim-FO-ma), brain cancer, and osteosarcoma (os-tee-o-sar-KOME-a) (bone cancer). Cancer is sometimes referred to as a malignancy or a malignant tumor.
How Does Cancer Begin?
With more than 100 types of cancer, the disease can arise in almost any part of the body. Each cancer is different, but they all start the same way. A healthy body is home to more than 10 trillion cells (at least 100 times as many stars as there are in the entire Milky Way galaxy). Just as neighbors cooperate to maintain an orderly community, cells usually grow, divide, and die in a controlled fashion. But cancer cells are renegades, bad neighbors in the cellular community. Cancer begins when a single cell starts to multiply inappropriately.
What turns a good cell bad? The operating instructions for everything that our cells do are contained in the genes, packets of information that we inherit from our parents. Genes are made of a substance called DNA. The function of genes is to make proteins, the building blocks of life that carry out the work of the genes. When a gene inside a cell is switched on, the cell starts producing the required protein. Sometimes genes become altered, and we say they have mutated. Mutations in a gene can affect how the gene works; for example, a mutated gene might produce too much of a protein, or perhaps none at all.
Life proceeds by cell growth and division, and this process is directed by a collection of genes whose proteins work like traffic cops to encourage growth, or to halt it. When these genes become mutated, the proteins they make may erroneously tell cells to continue growing, like a traffic light stuck on green. The mutated genes are called oncogenes. Normal cells with damaged DNA die. But cancer cells with damaged DNA may not.
Many tumors need 30 to 40 years to develop, which explains why children rarely get cancer. But it is possible for a person to inherit a mutant cancer-causing gene. When that happens, people sometimes get cancer at an earlier age.
Genes can undergo mutations as a result of cancer-causing substances called carcinogens (kar-SIN-o-jens) in the environment as well as chemicals in our own cells. Another source of mutations is copying mistakes that occur when DNA is replicated during cell division. Cells normally have repair systems to correct such errors. But when the repair system slips up, the damage becomes a permanent part of that cell and of the cell's descendants. If a person has a faulty repair system, mutations in the genes will build up rapidly, making the cells more likely to become cancerous. Faulty repair plays a role in certain kinds of colon, skin, and breast cancers.
The body's defenses are impressive, and it is difficult for cancer to get started. But imagine that a renegade cell has managed to evade every one of the cell's checkpoints and has formed a tumor. Now what? To grow larger than a millimeter (about the size of a pinhead), a tumor needs a blood supply, so it sends out a chemical signal to cause blood vessels to grow.
How Does Cancer Spread?
Normal cells do not wander. But some types of cancer cells do, which is what makes them so dangerous. The process is called metastasis (meh-TAS-ta-sis). Although it may be fairly easy to remove the main, or primary, tumor in cancer, metastasis cannot usually be cured by surgery alone.
In order for cancer to spread to other parts of the body, it must detach from its original location, invade a blood vessel, travel through the circulation to a far-away site, and set up a new cellular colony. At every one of these steps, it must outsmart the many controls the body has to keep cells where they belong.
New techniques show that abnormal cells from a tumor often are circulating even when doctors can find no evidence of spread. We call this undetectable spread micrometastasis (MY-kro-meh-TAS-ta-sis). Once a cancer cell has found a new home, it must reverse all the steps it took in liberating itself. It has to attach to the inner lining of a blood vessel, cross through it, invade the tissue beyond, and multiply. Probably fewer than 1 in 1,000,000 of the cancer cells that make it into the bloodstream survive to take up residence elsewhere.
Cancer cells "prefer" small blood vessels, and the first small blood vessels a freed cancer cell encounters are those of the lungs. So the lungs are the most common site of spread for cancer, followed by the liver. Much of how cancer spreads is still a mystery. Some tissues—for example, cartilage and brain tissue—seem more resistant to cancer. And some animals almost never have cancer.
What Causes Cancer?
A risk factor is anything that increases a person's chance of getting a disease. But having a risk factor does not mean that a person will get the disease for sure. People get cancer as a result of a complex set of interactions between their genes and the environment. We are just beginning to understand these reactions.
Tobacco
Tobacco is a lethal cancer-causing substance. It causes 30 percent of total cancer deaths every year in the United States, affecting the lungs and other organs of the body. Almost all lung cancer is the result of smoking. The younger a person starts to smoke, the greater the risk of cancer.
The U.S. and the World
The U.S. National Cancer Institute says that 8.4 million people—about 3 percent of the population in 1999—have a history of cancer. The death rates for most major cancers have declined since the 1970s, because of earlier detection and better treatment. About 2 million women are breast cancer survivors and 1 million men are prostate cancer survivors.
Still, cancers killed 539,577 Americans in 1997. This accounted for 23 percent of all deaths that year, making cancer the second leading cause of death after heart disease. Lung cancer caused the majority of the cancer deaths (29 percent), followed by stomach cancer (23.5 percent).
Each year, about 150 of every 1 million Americans under age 20 will be diagnosed with cancer. But the chances for surviving at least five years with cancer increased for children between the early 1980s (64 percent survived) and the early 1990s (74 percent). That is better than the five-year survival rate for all cancers, which was about 60 percent in the 1990s.
Worldwide, cancer caused an estimated 7.2 million deaths in 1998, which accounts for 13 percent of all deaths. Lung cancer was the leading cause, accounting for 17 percent of all cancer deaths.
Cancer deaths worldwide have increased slightly since 1993, when about 6 million people died of cancer. That represented 12 percent of all deaths worldwide in 1993.
About 81 million people worldwide were living with cancer in 1998. The World Health Organization (WHO) expects the prevalence of cancer cases to increase in the first 25 years of the twenty-first century in developing nations.
The World Health Organization estimates about 15 million new cases of cancer will develop in the year 2020, compared with 10 million new cases a year in the late 1990s. Reasons include increased smoking in developing nations, unhealthy diets, and more people living to old age, when cancer risk is higher.
The World Health Organization estimated in the mid-1990s that 15 percent of all cancers worldwide could be prevented by controlling infections. For example, more than 400,000 cases of liver cancer were tied to infection with hepatitis in the mid-1990s. Parasites in food also can lead to stomach cancers.
Other trends to watch between 1999 and 2025, according to WHO: Lung cancer and colorectal cancer cases and deaths will increase, largely because of increased smoking and unhealthy diet. Women will die in higher numbers from lung cancer in almost all industrialized countries. Stomach cancer is expected to become less common, because of improved food conservation, changes in diet, and declining infection. Cervical cancer is predicted to decrease in industrialized countries because of increased screening and it might decrease in the developed world if a vaccine is developed. And, finally, liver cancer will decrease as the rates of immunization and screenings for hepatitis increase.
Food and alcohol
In the United States, diet has been associated with certain cancers, particularly diets containing high amounts of animal (saturated) fat and red meat. After years of studies, coffee has not been proved to cause cancer, nor have artificial sweeteners. Eating insufficient quantities of fruits and vegetables appears to contribute to cancer, for reasons no one understands. It may be that fruits and vegetables help to block the cancer-causing effects of our own bodies. Drinking large amounts of alcohol increases the risk of cancer of the upper respiratory and digestive tracts, and alcoholic liver disease can lead to liver cancer. Even moderate drinking may contribute to breast and colon and rectal cancer.
Radiation
Some forms of radiation cause cancer. But most cancer deaths from radiation are caused by natural sources such as the sun's ultraviolet rays. For example, sunburns during childhood are a key factor in causing a kind of skin cancer called melanoma (mel-a-NO-ma). But electric power lines, household appliances, and cellular telephones have so far not been proven to cause cancer. Radiation from nuclear materials and reactions does cause cancer, but most people are not exposed to levels high enough to harm them.
Chemicals
In the past, some people who worked with certain chemical substances such as asbestos (az-BES-tos) and benzene (BEN-zeen) had a greater chance of getting lung cancers and other kinds of cancers. But strict government regulations have limited the use of these substances and sharply reduced the numbers of these cancers.
American Cancer Society
The American Society for the Control of Cancer (ASCC) was founded in 1911 to educate the public about the dangers of cancer. In 1943, Mary Lasker, the wife of an advertising tycoon who himself would die of cancer, walked into the office of Clarence C. Little, the managing director of the ASCC, and asked him how much money the society was spending on research. Nothing, Little told her.
Lasker immediately began a campaign to raise funds for the renamed American Cancer Society (ACS). A granting program was begun in 1946. By 1948, the ACS had raised around $14 million. Today, the ACS has chartered divisions throughout the country and over 3,400 local units. ACS is the largest source of private, not-for-profit research funds in the United States, second only to the federal government in total dollars spent.
How Do People Know They Have Cancer?
Many symptoms of cancer such as weight loss, fever, fatigue, and various kinds of lumps could also be caused by other diseases. Some cancers may cause no symptoms until they have spread. Based on the most commonly occurring cancers, the American Cancer Society publishes a list of seven warning signs of cancer. These symptoms do not mean that a person has cancer, but if they occur, a person should see the doctor:
Change in bowel or bladder habits (for instance diarrhea that does not go away or pain on urination)
A sore anywhere on the skin that does not heal
Unusual bleeding or discharge from the nose, mouth, skin, nipple, or vagina
A thickening or lump in the breast or elsewhere
Indigestion or difficulty in swallowing
Obvious changes in a wart or mole
Nagging cough, particularly if these symptoms occur in a cigarette smoker.
Eating for Health
The American Cancer Society recommends the following general nutritional guidelines to help people stay healthy:
Choosing most foods from plant sources such as vegetables, fruits, and grains
Limiting intake of high-fat foods, especially from animal sources
Staying physically active
Maintaining a healthy weight
Limiting consumption of alcoholic beverages
How Is Cancer Diagnosed and Treated?
Diagnosis
Diagnosing cancer involves removing some tissue for evaluation. This procedure is called a biopsy (BY-op-see). Once the diagnosis is made, a treatment plan is put together. To do that, it is necessary to determine how widespread the disease is, and how serious. "Staging" the disease means assigning letters and numbers to it as a way of indicating whether it has spread and how far. There are several systems for staging, depending on the type of cancer. Generally speaking, the smaller the tumor, the more curable it is, although some cancer can be unpredictable. The outlook for some cancers, for example, leukemia and lymphoma, is judged according to other criteria. Cancer is classified by the part of the body in which it began and by how it looks under a microscope.
Treatment
Treatment for cancer includes surgery, radiation, and chemotherapy (kee-mo-THER-a-pee), alone or together. Because different types of cancer vary in how fast they grow, where they spread, and how they respond to treatment, treatment is specifically tailored to the kind of cancer a person has.
Surgery is the oldest form of treatment for cancer, and it still offers the greatest chance of cure for many kinds of cancer. About 60 percent of patients with cancer will have some type of surgery.
Radiation therapy uses high-energy particles or waves to damage cancer cells that surgery cannot catch because they are too small.
Chemotherapy uses anticancer drugs to treat cancer. Chemotherapy drugs are given through a vein (also called an intravenous or IV line) or by mouth as pills. These drugs enter the bloodstream and reach places in the body that surgery and radiation cannot reach. Chemotherapy is often given for cancer that has spread.
Another kind of therapy interferes with the production of substances in the blood called hormones (HOR-mones) that stimulate certain kinds of cells (for example, cells in the breast) to grow.
Will There Ever Be a Cure for All Cancers?
Every day researchers learn a little more about how the cell works, and many of these discoveries are being applied to cancer research. Many current therapies have side effects because they kill healthy cells as well as cancer cells or affect the function of other parts of the body. So one area of research scientists are working on is therapies that will kill only cancer cells and that will leave healthy cells alone. Another area of research is investigating ways of helping the body's own defense system to fight cancer. Scientists are also exploring substances in food or drugs that will prevent cancer from developing in the first place.
Can Cancer Be Prevented?
In the United States, 1.2 million people are diagnosed with cancer each year. There is no way to prevent cancers children get. But many cancers that occur in adults could be prevented by changes in a person's lifestyle. For example, cancers caused by cigarette smoking and drinking a lot of alcohol could be prevented completely. Limiting certain kinds of foods, such as red meats and animal fats, and eating lots of fruits and legumes (such as peas and lentils) may help reduce the risk of getting many cancers. Physical activity helps to avoid obesity and may have other protective effects against cancer. Most of the one million skin cancers that are diagnosed each year could be avoided by staying out of the sun.
Regular cancer checks, called screenings, for cancer of the breast, colon, rectum, cervix, prostate, testes, mouth, and skin are an effective way of detecting cancer early enough to be treated successfully. In addition, self-examination for breast and skin cancers also helps to detect tumors at earlier stages. The American Cancer Society estimates that if all Americans participated in regular cancer screenings, survival would be dramatically improved.
Living with Cancer
A cancer diagnosis is usually shocking and frightening. A person's life is suddenly disrupted by surgery, treatment, visits to the doctors, and changing personal relationships. Children with cancer may have to miss school for a time or to give up sports or other activities. A person may feel anger at themselves or others, or at God. Children especially may feel that something they did caused the cancer, especially if it is a brother or sister who is sick. Family, physician, friends and organizations, religious groups and clergy, and self-help groups all may be an important source of support. Each person's way of dealing with cancer is unique. Even with cancers that will cause death, a person may live for many years. And more than 70 percent of children and adolescents with cancer are successfully treated.
Clinical Trials and New
Cancer Treatments
Studies of new or experimental treatments in patients are known as clinical trials. Research in cancer could not move forward without them because drugs may work very differently in people than in the animals in which the drugs first proved successful.
Clinical trials seek to answer such questions as:
Does this new treatment work?
Does it work better than other treatments already available?
Do the benefits outweigh the risks, including side effects?
Although there are risks to new treatments, clinical trials are done only when there is some reason to believe that the treatment will be of value to the patient.
Participating in a clinical trial is completely up to the patient. The doctor may suggest it, or patients can request information about clinical trials from the U.S. National Cancer Institute.
Alternative and complementary therapies
Many patients seek out other kinds of therapies during their treatment. Cancer is a frightening word, and some people will do anything, no matter how unlikely to work. A number of alternative treatments are themselves dangerous, and can distract from effective treatment. Some can be costly as well. These therapies generally are of two kinds:
Alternative therapies are often promoted in the mass media as cancer cures. Patients should be aware that these therapies have either not been tested for safety and effectiveness, or have been tested and found to be ineffective.
Complementary therapies, on the other hand, are used in addition to standard therapy. They may help to relieve symptoms of the disease or side effects of treatment, or they just may make patients feel better. Examples of complementary therapies are meditation to relieve stress and peppermint tea to combat nausea (stomach upset) from chemotherapy.
Patients who are thinking of using alternative or complementary therapies should first discuss it with their health care team.
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