Cancer Treatment

Cancer is a disease in which cells multiply wildly, destroy healthy tissue, and endanger life. About 100 kinds of cancer attack people. Cancer strikes people of all ages but is most common in the middle-aged and the elderly. The disease is a leading cause of death in many countries. Cancer occurs about equally in males and females. The disease can attack any part of the body and may spread to other parts. Cancer occurs in most other animals as well as in people.

The study of the development, treatment, and prevention of cancer is called oncology. It includes both research and clinical care. Physicians who specialize in oncology are known as oncologists.

Scientists have greatly increased their knowledge of how cancer develops. The cells of all living things contain genes that direct cell growth and reproduction. Cancer arises when these genes become damaged and cells multiply without control. The damaged genes may instruct the cell to divide in an abnormal fashion. Other genes may lose the ability to instruct the cell that it can no longer function and must die. Some damaged genes are changed in ways that enable cancer cells to invade healthy tissue, grow new blood vessels, or spread to other parts of the body.

Some types of abnormalities in genes are inherited. Substances in the environment can also damage genes. A substance that damages genes in a way that can lead to cancer is called a carcinogen. Many substances found in nature, both natural and artificial, are carcinogens.

Without proper treatment, most kinds of cancer are fatal. However, methods of diagnosing and treating the disease have improved greatly. About half of all cancer patients now survive at least five years after treatment. People who remain free of cancer during that time have a good chance of remaining permanently free of the disease.

More research is needed to find even better methods of curing cancer. Because cancer affects so many people, many countries spend public money to fund cancer research.

Cancers that affect human beings are classified in two ways: (1) by primary body site-that is, the part of the body where cancer first develops; and (2) by the type of tissue in which the cancer originates.

Classification by Primary Body Site
Cancer first appears most often in the skin, the female breasts, and the organs of the digestive, respiratory, reproductive, blood-forming, lymphatic, and urinary systems. The number of cases of cancer in these sites varies from country to country. Cancer of the stomach, for example, is much more common in Japan than in the United States or India. Rates of breast cancer are high in the United States and the United Kingdom, but much lower in India and many Asian countries. The following discussion deals with the kinds of cancer that occur most often in many countries.

Skin Cancer
Skin cancer is the most common type of cancer in the world. Most skin cancers grow slowly and do not spread to other parts of the body. As a result, these cancers are among the easiest to cure. Most people treated for skin cancer recover completely. However, one form of skin cancer called malignant melanoma is particularly dangerous. This type of cancer begins in the skin's pigment cells. If not detected and treated early, it can spread rapidly to other parts of the body.

Cancers of The Digestive Organs
Cancers of the digestive organs most commonly affect the parts of the large intestine called the colon and the rectum. About half of all people treated for cancer of the colon or rectum survive five years or longer after treatment with no return of the disease. Other digestive organs commonly affected by cancer include the esophagus, liver, pancreas, and stomach.

Cancers of The Respiratory System
Cancers of the respiratory system involve the larynx and lungs. In most industrial countries, lung cancer kills more people each year than any other kind of cancer. The death rate is high because many lung cancers have spread to other body sites before they are detected.

Breast Cancer
Breast cancer occurs in both sexes, but it attacks women about 100 times more often than it strikes men. Most of these cancers occur in women over 40 years of age. Female breast cancer patients whose disease is found and treated before it has spread beyond the breast have good long-term survival rates.

Cancers of The Reproductive System
Cancers of the reproductive system are relatively common among both men and women. The male organ most often affected is a small gland called the prostate. Most cases occur in men over 50 years old. Proper treatment can cure the disease in its early stages and control more advanced prostate cancer for many years.

The most common cancers of the female reproductive system affect the uterus, the organ in which babies develop. Some cancers arise in the main part of the uterus. Cancer may also affect the lower, necklike part of the organ called the cervix. Cancer of the cervix strikes more younger women than do other cancers of the uterus.

Cancers of The Blood-Forming and Lymphatic Systems
Cancer of the bone marrow and other blood-forming organs is called leukemia. In leukemia, immature white blood cells multiply wildly and interfere with production of other vital blood elements.

Cancer may also arise in tissues of the lymphatic system. This system is a network of vessels that returns fluids to the bloodstream and helps fight disease. Lymphatic cancer is called lymphoma. A well-known form of lymphoma is Hodgkin's disease, named after Thomas Hodgkin, the English physician who first described the disorder. Hodgkins disease affects both young adults and older individuals. The most common lymphatic cancer is non-Hodgkin's lymphoma. Cases of non-Hodgkin's lymphoma have risen steadily since the mid-1900's. Many people with AIDS develop this type of cancer.

Cancers of The Urinary System
The bladder is the urinary organ most commonly affected by cancer. The majority of bladder cancer patients are men, and most survive five years. Many such cancers are detected early because they arise in the inner layer of the bladder
and cause bleeding in the urine.

Classification by Tissue
Scientists group cancers based on the body tissue in which tumors begin. Carcinomas develop in epithelial tissue, which forms the outer layer of skin and lines internal body surfaces and organs. Many organs, including the breast, colon, and lung, also contain glands. Cancers that arise in gland tissue, called adenocarcinomas, are among the most common cancers.

Cancers that develop in connective tissue are called sarcomas. Connective tissue forms the body's supporting structures, such as bones and cartilage. Sarcomas also form in the breast, digestive system, respiratory system, and reproductive system, but far less often than carcinomas.

Cancer in children, called pediatric cancer, differs from adult cancer in several ways. Cancers common in adults, such as those that occur in the lungs, breasts, prostate, or colon do not usually occur in children. The common types of cancer that strike children include neuroblastoma, which arises in nervous tissue; retinoblastoma, which develops in the eyes; nephroblastoma, also called Wilm's tumor, which occurs in the kidneys; rhabdomyosarcoma, which arises from soft tissues; and osteogenic sarcoma and Ewing's sarcoma, which develop in the bones. These cancers are extremely rare in adults.

The emotional impact on the family and physical and emotional consequences to the child are important considerations in the treatment of pediatric cancer. Fortunately, many of these cancers and leukemias are highly curable, and many children survive to lead normal lives following treatment. However, the treatment of pediatric cancer may have long-term consequences for patients as they live out normal life spans. For example, radiation therapy and chemotherapy can actually cause secondary cancers, including leukemia, years after treatment has been completed. Other long-term consequences of cancer treatment may include stunted growth and infertility later in life.

Scientists have found that the cells of pediatric cancers often show specific genetic abnormalities. These abnormalities have given researchers a better understanding of the genetic difference between normal cells and cancer cells.

Scientists know that many cancers have a genetic cause which limits their ability to prevent the disease. However, scientists have identified several factors that can increase a person's chances of developing cancer. They have also discovered substances that may protect DNA and keep cancer from developing. Many scientists believe that people can decrease their overall chances of developing cancer by adopting a healthy lifestyle and avoiding contact with known carcinogens.

Avoiding Carcinogens
Smoking is one of the most widespread and avoidable environmental causes of cancer. Scientists think that smoking causes about one-third of all cases of cancer, including most lung cancers. Smoking also causes many cancers of the mouth, larynx, trachea, esophagus, pancreas, kidney, bladder, and cervix. Cigarette smoke can even cause cancer in nonsmokers who live or work closely with smokers. Smokers who quit can significantly reduce their chance of developing lung cancer.

People can also reduce their risk of developing skin cancer. The sun is one of the most important sources of cancer-causing radiation. Most cases of skin cancer-including deadly melanoma-are caused by an invisible portion of the sun's radiation called ultraviolet rays. Physicians advise against sunbathing and recommend that people who work outdoors wear protective clothing or apply sunscreens that block ultraviolet rays.

Nutrition
Some chemicals naturally present in food may become a cancer threat if consumed in large quantities. Diets high in fats, for example, have been associated with cancers of the breast, colon, and prostate gland. Some studies have linked eating large amounts of salt-cured, salt-pickled, and smoked foods to cancers of the digestive system. Excessive alcohol consumption has been linked to cancer of the mouth, pharynx, larynx, esophagus, and liver.

Many scientists believe that certain foods contain substances that may help prevent cancers in people. Such foods include broccoli, cauliflower, cabbage, spinach, tomatoes, carrots, fruits, and whole-grain breads or cereals.

Every person begins life as a single fertilized egg cell. Through a complicated process of growth, division, and specialization, the egg multiplies into the trillions of cells in a healthy body. Every cell contains complex instructions that direct this process. The instructions are chemically coded in long coils of a substance called DNA (deoxyribo nucleic acid). Particular sections of DNA make up genes that control specific cell functions. DNA even contains genes that enable the molecule to repair itself. But as people grow older, damage can build up and destroy DNA's ability to repair itself.

Cancer often results from damage to the genes that control cell growth and division. Two important classes of these genes are called proto-oncogenes and suppressor genes. Proto-oncogenes promote cell growth or division. Damage to a proto-oncogene may transform it into an overactive form called an oncogene. Oncogenes can lead to cancer by directing a cell to multiply excessively. Scientists have identified dozens of oncogenes that contribute to cancers in many sites, including the bladder, breasts, liver, lungs, and colon.

Suppressor genes limit cell growth or division. Damage to a suppressor gene can lead to cancer by destroying that gene's ability to stop cell multiplication.

Scientists think most cancers involve transformation of many proto-oncogenes into oncogenes and inactivation of a number of suppressor genes. In most cases, genetic damage must accumulate for years before a cell becomes cancerous. Once cancer occurs, the disorganized, rapidly dividing cells gradually build up into a mass that compresses and destroys nearby tissue. As the cancer grows, cells can break away and travel through blood or lymph (fluid from body tissues) to invade other parts of the body. This spread of cancer to other sites is called metastasis. The likelihood of curing cancer drops sharply after the tumor has spread.

People acquire the genetic damage that can lead to cancer in two main ways: (1) by inheriting damaged genes; and (2) through exposure to substances in the environment that damage genes.

Scientists have long known that the risk of some cancers increases for people with close relatives who also have the disease. This increased risk occurs because some types of genetic damage involved in cancer can be passed from parents to children. But most cancers require multiple injuries to DNA. Inherited damage to one gene thus raises risk but does not guarantee that any particular individual will develop cancer. Scientists have identified the inheritable genetic damage involved in certain forms of breast, colon, and other cancers. Researchers are working to learn much more about inherited cancer genetics. They hope their knowledge will lead to new strategies for preventing and treating cancer.

Most people who develop cancer do not have inherited genetic abnormalities. Their genes are damaged after birth by carcinogens in their environment.

Scientists identify carcinogens by investigating unusually high cancer rates in groups of unrelated people. For example, scientists might notice that people in a particular job tend to get a certain type of cancer. Experts would then study the ability of chemicals or other substances encountered in that job to cause cancer in laboratory animals. If a high percentage of the animals develop cancer, researchers strongly suspect that the agent may also cause cancer in people.

Once a carcinogen damages a cell's DNA, the damage can be passed on to new cells that arise from division of the damaged cell. The changes are thus passed on to all the cell's descendants. Meanwhile, the descendant cells can acquire additional DNA damage that is also passed along. Experts think many cancers arise from such combined effects of several carcinogens.

Three classes of carcinogens in human beings are (1) chemicals, (2) certain forms of radiation, and (3) viruses.

1. Chemicals
Scientists have identified many chemicals that can cause cancer in animals. These chemicals may also pose a cancer hazard to human beings. For example, cigarette smoke contains more than 4,000 chemical substances, of which dozens have been identified by scientists as carcinogens.

Some industrial chemicals create a cancer hazard for people who work with them. Such chemicals include aniline dyes, arsenic, asbestos, benzene, chromium, nickel, vinyl chloride, and certain products of coal, lignite, oil shale, and petroleum. Scientists work continuously to find chemicals that pose occupational cancer risks. Such identification can help ensure a safe workplace and identify substances that may also pose a risk to the general population.

Some substances that are added or applied to foods are also suspected of causing cancer in human beings. These substances include some chemicals used to control weeds and some that are used to kill insects. Government agencies regulate many of these substances, and, in some cases, prohibit their use. Molds that sometimes develop on such food crops as corn and peanuts may also contain carcinogens. The mold can be controlled through proper storage and handling of crops.

2. Radiation
Certain kinds of radiation can disrupt DNA and lead to cancer. X rays are a cancer hazard in large doses. However, doctors do not believe that routine medical and dental X rays pose a significant danger. A form of nuclear radiation known as ionizing radiation can also cause cancer. For example, in 1986, when Ukraine was part of the Soviet Union, a nuclear reactor at a power plant in Chernobyl exploded. Children who were exposed to radioactive fallout from that explosion have experienced an increased rate of thyroid cancer.

3. Viruses
Experiments have shown that certain kinds of viruses cause cancer in animals. Some viruses can also cause cancer in people. For example, the human papilloma virus causes most cases of cervical cancer. Another virus has been linked to a rare form of leukemia, and some forms of liver cancer may be caused by viruses. However, most experts feel that viruses are not a major cause of human cancers.

Many cancers cause no symptoms in their early stages. To detect early cancers, the American Cancer Society recommends that people aged 20 to 40 have a cancer-related checkup by a physician every 3 years. People aged 40 or older should have a checkup every year. A cancer-related checkup usually includes a physical examination. Physicians watch carefully for any visible signs of cancer when they perform physical examinations.

Depending on the patient, screening tests for specific types of cancer may also be performed. Screening tests may include a breast X ray called a mammogram to detect breast cancer in women. A mammogram can detect some breast cancers before any lumps can be felt.

Physicians recommend that beginning at age 50, patients have routine tests for colon cancer. In one such test, called a fecal occult blood test (FOBT), the patient uses special kit to collect tiny samples of stool (solid body wastes). Laboratories test the samples for microscopic amounts of blood, which may indicate cancer.

The Pap test, another recommended yearly test for women, has greatly reduced the death rate from cancer of the uterus. In the Pap test, experts examine cells scraped from the cervix under a microscope. Microscopic signs of cancer can be seen 5 to 10 years before symptoms appear.

A blood test for a protein called prostate-specific antigen (PSA) may detect early prostate cancer. PSA is made only in the prostate gland. Elevated levels of the protein may mean that the gland has become cancerous.

The various methods of preliminary diagnosis may reveal the presence of a tumor. But not all tumors are cancerous. Most lumps in the breast, for example, are benign (noncancerous). Doctors need to perform a test called a biopsy to make a definite diagnosis of cancer. In a biopsy, doctors remove a small piece of tissue from the tumor. In suspected cases of leukemia, they take a blood sample or remove tissue from a blood-forming organ. Experts then examine the tissue under a microscope to check for cancer cells.

Preliminary diagnosis identifies a suspicious mass or other change in the body that requires further investigation. Some symptoms must be evaluated with special X rays and other advanced imaging techniques. One X-ray technique, called computed tomography or CT scan, can reveal suspicious masses in such internal organs as the brain and the lungs. A technique called magnetic resonance imaging (MRI) uses magnetic fields and radio waves to produce images of internal organs. These imaging techniques allow physicians to determine the exact location, size, and shape of cancer tumors and determine whether the cancer has spread.

Physicians use a process called staging to describe how a particular cancer in a patient has advanced. Staging is important in helping physicians decide which treatments are most likely to be successful in treating the cancer. The most common staging method is known as the TNM system. This system describes the tumor (T), whether the cancer has invaded lymph nodes (N), and whether there are any metastases (M). Physicians determine the staging level through physical examination, X rays, CT scans, and other specialized tests.

Since each type of cancer is different, there are different staging categories for each cancer. If cancer is discovered in the early stages, the cancer treatment may be successful. Advanced stage cancers are more difficult to treat. If tests show that the cancer has spread, patients may need to undergo additional treatments.

Pap test is a procedure for detecting cancer cells and abnormalities that could become cancerous in the female genital tract. It is most commonly used to evaluate the condition of the cervix, which includes the bottom portion and the opening of the uterus. The test is also called the Papanicolaou test and Pap smear test. George Papanicolaou, a Greek-born physician, developed the procedure in the United States from the 1920's to the 1940's. Widespread use of the Pap test has helped to greatly reduce the death rate from cancer of the cervix.

Before cancer develops in the cervix, the cells of the cervix go through many precancerous changes. These changes typically take several years. If a woman has Pap smear screenings regularly, precancerous abnormalities and early stages of cancer can be detected while these problems can be easily treated. With regular follow-up examinations, the woman can usually avoid developing invasive cancer (cancer that grows deeply into tissues).

A Pap smear can be performed in a physician's office. The procedure causes no pain and little discomfort. The physician collects a sample of cells from the cervix with a cotton swab, wooden scraper, or small brush. The physician then places the sample on a glass slide and sends it to a medical laboratory for examination. If abnormal cells are detected, the physician may examine the cervix through a type of microscope called a colposcope. If the physician finds abnormalities, a biopsy (removal and examination of tissue) will be performed to reach a diagnosis.

Women 18 years of age or older should have Pap smears taken annually. If a girl has sexual intercourse before the age of 18, she should begin having Pap smears earlier. Women who have had an abnormal Pap smear may need to be tested more frequently than once a year.

Breast cancer is an uncontrolled, potentially deadly division of cells in the breast. In the United States, breast cancer is the most common women's cancer. According to the American Cancer Society and the National Cancer Institute, an average of 1 American woman in 8 will develop breast cancer sometime during her life. Women in Africa and Asia have a lower risk of breast cancer than do women in North America and Europe. A small number of men also develop breast cancer.

The risk of breast cancer increases for all women as they grow older. A woman's risk also increases if a relative, especially her mother or a sister, has also had the disease. Scientists have found two rare abnormal genes, called BRCA1 and BRCA2, that greatly increase risk. Tests to detect these genes are available, but doctors disagree about when such tests should be used. Most women with one or two relatives who have had breast cancer do not have inherited genetic abnormalities.

A painless lump is the most common symptom of breast cancer. Doctors advise women to examine their own breasts for lumps every month. A breast X ray called a mammogram can detect many cancers before they can be felt. Most doctors recommend an annual mammogram for women over 50 years old.

Doctors usually begin treatment of breast cancer by surgically removing the tumor. When the cancer is small, a lumpectomy can preserve the breast. In this operation, a surgeon removes the cancerous lump and a margin of the normal tissue surrounding it. The breast is then treated with radiation to kill stray cancer cells. If the cancer is large, the entire breast must often be removed in a modified radical mastectomy .

In either a lumpectomy or a mastectomy, doctors also remove and examine lymph nodes from the armpit. These nodes are small masses of tissue that help the body fight disease by filtering out bacteria and other harmful particles. Cancer in the lymph nodes indicates a high risk that the tumor will reappear in other parts of the body. A tumor that is especially large or has extremely disorganized cells may also increase risk of renewed cancer even if the lymph nodes are healthy. If the tumor will likely reappear, doctors offer additional treatments.

To determine the best treatment, doctors test some cancer cells to see if female hormones make them grow. If the cells respond, doctors may prescribe the drug tamoxifen to block the action of these hormones. If hormones have no effect, or if the patient still has menstrual periods, doctors may use chemotherapy (drugs that have a toxic effect on a disease). Both tamoxifen and chemotherapy significantly reduce the risk of cancer returning.

Cervical cancer is uncontrolled multiplication of cells in a woman's cervix. The cervix includes the lower portion and opening of the uterus, the hollow, muscular organ in which a baby develops. Throughout the world, cancer of the cervix is an extremely common cancer of the female reproductive system. But it is a cancer that can be diagnosed and cured in its early stages.

Cervical cancer arises in cells of the epithelium, a type of tissue that covers the cervix. The first phase of the disease is called cervical intraepithelial neoplasia and often abbreviated CIN. In CIN, cells of the epithelium look abnormal under a microscope but have not yet become cancerous.

Untreated CIN may progress to a phase known as preinvasive. The progression usually occurs over 5 to 10 years but may take less than a year. Preinvasive neoplasia has not yet spread from the epithelium into deeper tissues of the cervix. The preinvasive phase may then progress to invasive cancer. Invasive cancer extends into layers of cervical tissue beneath the epithelium. In the most advanced cases, it reaches other organs or even distant parts of the body.

A simple, painless office procedure called a Pap test can detect all stages of cervical cell abnormalities. If a Pap test reveals abnormalities, doctors usually examine the cervix with a type of microscope called a colposcope. Tissue samples from suspicious areas provide a definite diagnosis.

Doctors can treat most cases of CIN or preinvasive neoplasia by removing only the affected cervical tissue. Removal methods include surgery, laser vaporization, and cryotherapy (freezing). Women with no future plans to have children may be treated with a hysterectomy (removal of the entire uterus).

In most cases, doctors can cure invasive cervical cancer with either a radical hysterectomy (surgery that removes the uterus and nearby lymph nodes) or with radiation. Radiation combined with chemotherapy (treatment with drugs) can also cure many tumors that extend to nearby organs. Cancer that has spread to distant parts of the body can rarely be cured but may be controlled for some time with chemotherapy.

The most common cause of cervical cancer is infection with human papilloma virus (HPV). This virus is transmitted during sexual intercourse. Smoking cigarettes or inhaling second-hand smoke increases the risk of infection. Having sex during early adolescence also increases risk, because the cervical epithelium is more easily infected in young women. Having sex with multiple partners raises risk, as does having sex with one partner who has had many other partners. In 2002, scientists announced progress in developing a vaccine that is effective against HPV and which may be used to prevent cervical cancer caused by the virus.

Colon cancer is the common name for an uncontrolled division of cells in the large intestine. Many doctors prefer the term colorectal cancer, because the disease most often affects the main part of the large intestine, called the colon, and the last part, called the rectum.

Colorectal cancer is one of the most common cancers in North America and Europe, but it is relatively rare in Asia and Africa. The difference may be due to regional variations in diet. Studies show that people may help avoid this disease through a diet that is low in fat and rich in fruits and vegetables. Other studies suggest that small doses of aspirin at least every other day may also help prevent colorectal cancer.

Conditions that inflame the intestine, such as ulcerative colitis, increase a person's risk of developing colorectal cancer. People who have family members with that type of cancer also have an increased risk. Scientists have identified abnormalities in particular genes (the hereditary material in cells) that are associated with some rare forms of the disease. Experts believe that many common types of colorectal cancer also involve genetic abnormalities. Cancer often arises in polyps, small noncancerous growths in the intestine. A tendency to develop polyps is probably influenced by genes, as well.

In its early stages, cancer in the right side of the large intestine may not cause noticeable symptoms. Cancer that develops in the left side of the colon or the rectum often affects an individual's bowel habits. People should see a doctor if they experience any change in the frequency of their bowel movements or pain while having a movement. Stools (solid body wastes) that look unusually narrow or appear to contain blood should also be evaluated.

Many doctors recommend that middle-aged people have routine tests for colorectal cancer. Doctors often give such patients special kits to collect tiny samples of stool as part of their regular checkups. Laboratories test these samples for microscopic amounts of blood, which may indicate cancer. Periodic examinations with special instruments that enable doctors to see inside the intestine are also recommended. During these examinations, doctors can obtain samples of suspicious tissue, which can be checked under a microscope for cancer cells.

Most patients whose cancer is confined to the intestine have the growth surgically removed. They may also receive radiation therapy or chemotherapy (treatment with drugs). These patients have an excellent chance of being cured. Patients whose cancer has spread beyond the intestine usually have surgery, supplemented by radiation therapy or chemotherapy.

Hodgkin's disease is a type of cancer in which the lymph nodes become. Other lymphoid tissues, such as the spleen, also may become swollen. Most victims of Hodgkin's disease are 20 to 40 years old. The disease, which strikes more men than women, may be fatal. Its cause is unknown.

Beginning in the 1960's, medical researchers discovered much about Hodgkin's disease and how to control or even conquer it. They learned that the disease (1) spreads in a fairly predictable way from one group of lymph nodes to the next; (2) takes a relatively long time to spread to other areas of the body; (3) can usually be treated successfully with radiation in early stages; and (4) can often be treated successfully with drugs in advanced stages. Hodgkin's disease resembles other diseases that also cause swelling of the lymph nodes. Physicians identify the condition by the presence in the swollen tissue of large cells called Reed-Sternberg cells. Most of these large cells have two nuclei. Hodgkin's disease was first described by Thomas Hodgkin, an English physician, in 1832.

Leukemia is a cancer of the bone marrow, which is the soft, spongy, blood-forming tissue within bones. Bone marrow produces three types of blood cells: (1) white blood cells that fight infections; (2) red blood cells that carry oxygen from the lungs to the rest of the body; and (3) platelets, tiny blood cells that help stop bleeding. In leukemia, large numbers of abnormal white blood cells multiply in an uncontrolled manner in the bone marrow and crowd out normal blood cells. In addition, the abnormal white blood cells do not fight infections.

Symptoms of leukemia include fevers and infections. Fatigue, anemia (a lack of functioning red blood cells), and bleeding or bruising due to low platelet count are also among the symptoms of the disease.

Leukemia is classified as acute or chronic, depending on how quickly it develops. The disease is also classified by the type of white blood cells affected. The most common types of white blood cells are lymphoid and myeloid, and each kind fights certain infections. When leukemia affects lymphoid cells, it is called lymphocytic leukemia. Leukemia that affects myeloid cells is called myeloid or myelogenous leukemia. Both lymphocytic and myeloid leukemia may be acute or chronic.

Acute leukemias develop extremely quickly. Abnormal, immature white blood cells multiply rapidly, and the number of normal cells decreases sharply. Acute lymphocytic leukemia is the most common leukemia in children. About 70 percent of children with this leukemia can be cured with current treatments.

The most common treatment for acute lymphocytic leukemia is chemotherapy, the use of chemicals to kill the cancer cells. Radiation therapy may be combined with chemotherapy to treat this leukemia. Radiation therapy uses high-energy X-rays to kill cancer cells. Another treatment is bone marrow transplant, in which the diseased bone marrow is destroyed and replaced with healthy bone marrow from a donor.

All treatments for acute leukemias are intensive and may endanger the patient's life. The use of powerful antibiotics and of blood transfusions has increased the chances of surviving the intensive therapy.

Acute myeloid leukemia usually strikes adults. Chemotherapy is the preferred treatment for this leukemia. Seventy percent of patients receiving chemotherapy enter remission. During remission, the blood cells and bone marrow return to normal. Patients are considered cured if they remain in remission for at least two years. However, only 25 percent of patients with acute myeloid leukemia remain in remission and are cured.

Chronic leukemias develop more slowly than acute leukemias. In chronic leukemias, the abnormal white blood cells appear mature and resemble normal white blood cells. In the early stages of the disease, the abnormal cells even function normally. Chronic lymphocytic leukemia is the most common leukemia among adults. The disease may take as long as 10 years to develop. This leukemia typically changes within several years into an acute leukemia that is resistant to most treatments. Chronic myeloid leukemia also occurs primarily in adults.

The cause of most leukemia is unknown. Possible causes include genetic abnormalities and exposure to radiation or certain chemicals. In patients with chronic myeloid leukemia, sections of two chromosomes have switched places. This switch leads to the production of an enzyme that triggers cell growth. Scientists have created a drug that blocks the action of the enzyme. The drug, marketed as Gleevec, is highly effective for treating chronic myeloid leukemia. By targeting the abnormality that causes the growth of the leukemia cells, Gleevec kills only leukemia cells. As a result, side effects of the treatment are minimal. Scientists are working to identify all the molecular abnormalities of each type of leukemia so that similar treatments can be developed.

Lung cancer is an uncontrolled, extremely deadly division of cells in the lung. In most developed countries, it kills more men and women than any other form of cancer. The death rate is high because many lung cancers have spread through the body by the time symptoms appear. Once lung cancer has spread, it is extremely difficult to cure.

Smoking causes most cases of lung cancer. The risk of developing lung cancer increases according to the length of time and the amount a person smokes. Exposure to secondhand smoke also increases risk. Other causes include long-term exposure to a radioactive gas called radon or to airborne asbestos fibers .

Symptoms of lung cancer include persistent cough, weight loss, shortness of breath, coughing up blood, chest pain, or a hoarse voice. If lung cancer is suspected, doctors may begin their examination by examining a patient's sputum (coughed-up material) for cancer cells. Patients may also have a chest X ray to reveal suspicious masses or other signs of lung disease.

Doctors further investigate abnormal lung areas by obtaining a biopsy (sample of tissue) and examining it under a microscope. In one biopsy procedure, doctors pass a thin, lighted tube called a bronchoscope into the bronchi. The bronchi are the lung's breathing tubes, where most cancers form. Doctors can test other lung parts with a technique called video thoracoscopy. In this technique, tiny cameras inserted into the chest send detailed pictures to a big screen, enabling doctors to find and sample abnormalities.

If diagnostic tests show cancer, doctors identify the type of lung cell from which the cancer developed. The various types of cells respond differently to treatments. Treatment also depends on whether the cancer has spread beyond the lung. Many lung cancers spread first to lymph nodes in the chest. These nodes are small masses of tissue that help fight disease by filtering out bacteria and other harmful particles. Other sites invaded by lung cancer include bones, the brain, and the liver.

Doctors can sometimes cure patients whose cancer has not spread. If cancer appears confined to the lung and the patient is otherwise healthy, surgeons usually remove all or part of the lung. During surgery, doctors also remove lymph nodes and test them for cancer cells.

Few patients whose cancer has spread can be cured. Treatment of these patients aims at extending life and reducing pain. Doctors may prescribe drug treatments-called chemotherapy-or radiation therapy to try to shrink tumors and relieve symptoms.

Prostate cancer is an uncontrolled division of cells in the prostate gland, a walnut-sized internal organ of the male reproductive system. In the United States, prostate cancer kills more men than any other cancer except lung cancer. African American men have the highest rate of prostate cancer in the world. Individuals have an increased risk of prostate cancer if other men in their families have also had the disease.

A cancerous prostate gland may become enlarged and press on the urethra, the tube through which urine leaves the body. The expanding gland may also put pressure on the bladder. Many prostate cancer patients consult a doctor because this pressure causes frequent urination or difficulty passing urine.

Doctors must perform tests to determine if these symptoms are due to cancer or to noncancerous enlargement of the prostate, another common condition. The first such test is often a digital rectal examination. In this procedure, a doctor feels the prostate gland directly by inserting a finger, covered with a lubricated glove, into the patient's rectum. A lump or an area of hardness may indicate cancer. Another means of diagnosing prostate cancer is a blood test that measures a protein called prostate-specific antigen (PSA). Elevated levels of PSA, which is produced only in the prostate gland, may indicate cancer.

A suspicious digital exam or PSA test is often followed by an ultrasound examination, which uses sound waves to create a detailed image of the prostate. This image aids a doctor in obtaining small surgical samples of tissue from the gland. If the tissue is cancerous, more tests are needed to determine if the cancer is confined to the prostate or has spread elsewhere in the body.

Doctors can often cure cancer that remains confined to the prostate by radiation therapy or by surgical removal of the gland. Both treatments may interfere with a man's ability to have sexual relations or may cause urinary incontinence (inability to hold back urine). Surgeons have developed an operation that may avoid sexual problems by preserving nerves important in sexual functioning. Doctors extend the lives of patients whose cancer has spread beyond the prostate gland with treatments that reduce levels of male hormones. Prostate cancer cells need male hormones to survive and grow.

Doctors recommend that middle-aged men have an annual digital rectal examination to detect any prostate cancer before it causes symptoms. Many doctors also recommend an annual PSA test, which can detect small tumors before they can be felt. Some doctors fear that this use of the PSA test will find some slow-growing cancers that would never become life-threatening. Treating such cancers may subject patients to the risks of unnecessary surgery or other procedures. But doctors cannot yet predict which tumors will become life-threatening.