Cancer





Definition

Cancer is a group of diseases characterized by uncontrolled growth of tissue cells in the body and the invasion by these cells into nearby tissue and migration to distant sites.

Description

Cancer results from alterations (mutations) in genes that make up DNA, the master molecule of the cell. Genes make proteins, which are the ultimate workhorses of the cells, responsible for the many processes that permit humans to breathe, think, and move, among other functions. Some of these proteins control the orderly growth, division, and reproduction of normal tissue cells. Gene mutations can produce faulty proteins, which in turn produce abnormal cells that no longer divide and reproduce in an orderly manner. These abnormal cells divide uncontrollably and eventually form a new growth known as a tumor or neoplasm. A healthy immune system can usually recognize neoplastic cells and destroy them before they divide. However, mutant cells may escape immune detection and become tumors or cancers.

Studies of the origins of cancer have shown that a combination of genetic influences and environmental causes over time triggers gene mutations, which may explain why most cancers are seen in adults of middle age or older (60%) and cancer is rare children. Many cancers have been shown to result from exposure to environmental toxins (carcinogens) and related alterations in DNA. Faulty DNA can also be inherited, predisposing an individual to develop cancer, although fewer than 10 percent of cancers are purely hereditary. Hereditary links have been shown in cancers of the breast, colon, ovaries, and uterus. Inherited physiological traits can also contribute to cancer, such as inheriting fair skin increasing the risk of skin cancer, but only if accompanied by prolonged exposure to intensive sunlight.

Tumors can be benign or malignant. A benign tumor is not cancer. It is slow growing, does not invade surrounding tissue, and once removed, does not usually recur. A malignant tumor is cancerous. It invades surrounding tissue and spreads to nearby or distant organs (metastasis). If the cancer cells have spread to surrounding tissue, even after the malignant tumor is removed, it will typically recur.

Cancer falls into several general categories:

  • Carcinoma (90% of all cancer) are solid tumors arising in the layer of cells (epithelium) covering the body's surface and lining internal organs and glands. Adenocarcinomas develop in an organ or gland and squamous cell carcinomas originate in the skin.
  • Melanoma originates in the skin, usually in pigment cells (melanocytes).
  • Sarcoma is cancer of supporting tissue such as bone, muscle, and blood vessels.
  • Leukemias and lymphomas are cancers of the blood and lymph glands.
  • Gliomas are cancers of the nerve tissue.

The most common cancers affecting adults are cancer of the skin, lung, colon, breast, and prostate. Cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and the leukemias and lymphomas are among the 12 major cancers affecting Americans of all ages. Although children and adolescents do develop solid tumors, the most common high-risk cancers among children are:

  • acute myeloid leukemia
  • acute lymphoblastic leukemia
  • neuroblastoma
  • glioma
  • sarcoma of bone (osteosarcoma) and soft tissue

Demographics

Childhood cancer is rare, occurring in about 14 in 100,000 children in the United States each year. However, in the entire U.S. population, one of every four deaths is from cancer, second only to deaths from heart disease. About 1.2 million cancer cases are diagnosed annually and more than 500,000 die, of whom 2,700 are children or adolescents.

Causes and symptoms

Genetic predisposition, environmental causes, and individual developmental problems are responsible for most childhood cancer. The presence of other disorders, such as Down syndrome , has also been shown to be associated with cancer in children. The major risk factors that apply to adult cancer are tobacco, alcohol, sexual and reproductive behavior, and occupation, none of which increases risk in children. Other well-known risk factors, such as family history, infectious agents, diet, environmental toxins, and pollution, can apply equally to children.

Tobacco

Approximately 80 to 90 percent of lung cancer cases occur in smokers. Smoking is also the leading cause of bladder cancer and has been shown to contribute to cancers of the upper respiratory tract, esophagus, larynx, kidney, pancreas, stomach, and possibly breast as well. Second-hand smoke (passive smoking) has been shown to increase cancer risk in children and adults who live with smokers.

Infectious agents

Cancer deaths worldwide can be traced to viruses, bacteria, or parasites. Epstein-Barr virus (EBV), for example, is associated with lymphoma, the hepatitis viruses are associated with liver cancer, HIV is associated with Kaposi's sarcoma, and the bacteria Helicobacter pylori is associated with stomach cancer.

Genetic predisposition

Certain cancers such as breast, colon, ovarian, and uterine cancer recur generation after generation in some families. Eye cancer ( retinoblastoma ), a type of colon cancer, and early-onset breast cancer have been shown to be linked to the inheritance of specific genes.

Environmental sources

Radiation is believed to cause 1 to 2 percent of all cancer deaths. Ultraviolet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x-rays, radon gas, and ionizing radiation from nuclear material.

Pollution

Studies have established links between environmental toxins, such as asbestos, and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollutants occurs when toxic industrial chemicals are released into the surrounding environment. As of 2004 an estimated 1 percent of cancer deaths are believed to be due to air, land, and water pollution.

Cancer is a progressive disease that goes through several stages, each producing a number of symptoms. Early symptoms can be produced by the growth of a solid tumor in an organ or gland. A growing tumor may press on nearby nerves, organs, and blood vessels, causing pain and pressure that may be the first warning signs of cancer. Other symptoms can include sores that do not heal, growths on the skin or below the skin, unusual bleeding, difficulty digesting food or swallowing, and changes in bowel or bladder function. Fever can be present as well as fatigue and weakness.

When to call the doctor

Despite the fact that there are hundreds of different types of cancer, each producing different symptoms, the American Cancer Society has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough , hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty swallowing
  • any change in bowel or bladder habits

Parents should report any such symptoms to the pediatrician along with unexplained fever or frequent infections. Vision problems, weight loss, lack of appetite, depression, swollen glands, paleness, or general weakness are other reasons for parents to consult the pediatrician. Generally, the earlier cancer is diagnosed and treated, the better the chance of a cure, although not all cancers have early symptoms.

Diagnosis

Diagnosis begins with a complete medical history, including family history of cancer, and a thorough physical examination. The doctor observes and palpates (applies pressure by touch) different parts of the body in order to identify any variations from normal size, feel, and texture of an organ or tissue. The doctor looks inside the mouth for abnormalities in color, moisture, surface texture, or the presence of any thickening or sores in the lips, tongue, gums, the roof of the mouth, or the throat. The doctor observes the front of the neck for swelling and may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland at the base of the neck, looking for nodules or tenderness. The doctor also palpates the lymph nodes in the neck, under the arms, and in the groin, looking for enlargement. The skin is examined for sores that are slow to heal, especially those that bleed, ooze, or crust; irritated patches that may itch or hurt; and any change in the size of a wart or a mole.

In adolescent females, a pelvic exam may be conducted to detect cancers of the ovaries, uterus, cervix, and vagina. The doctor first looks for abnormal discharges or the presence of sores. Then the internal pelvic organs such as the uterus and ovaries are palpated (touched while applying gentle pressure) to detect abnormal masses. Breast examination evaluates unevenness, discoloration, or scaling; both breasts are palpated to feel for masses or lumps.

In adolescent males, inspection of the rectum and prostate may be included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for growths, tumors, or other abnormalities. The testes are examined visually, looking for unevenness, swelling, or other abnormalities. The testicles are palpated to identify lumps, thickening or differences in size, weight, or firmness.

If an abnormality is detected on physical examination, or symptoms suggestive of cancer are noted, diagnostic tests will be performed. Laboratory studies of sputum, blood, urine, and stool can detect abnormalities that may confirm cancer. Sputum cytology involves the microscopic examination of phlegm that is coughed up from the lungs. Tumor markers, specific proteins released by certain types of cancer cells, can be detected by performing a test on venous blood. If leukemia or lymphoma is suspected, a complete blood count (CBC) with peripheral smear (differential) is done to evaluate the number, appearance, and maturity of red blood cells (RBCs) and white blood cells (WBCs) and to measure hemoglobin, hematocrit, and platelet count . A bone marrow biopsy may be done to determine what type of cells is present in the bone marrow. Blood chemistries will be done to help determine if liver or kidney problems are present. Blood chemistries are also useful in monitoring the effectiveness of treatment for all types of cancer and in following the course of the disease and detecting recurrences.

Diagnostic imaging techniques such as computed tomography (CT scans), magnetic resonance imaging (MRI), ultrasound, and fiberoptic scope examinations (such as colonoscopy or sigmoidoscopy) can help determine the location, size, and characteristics of a tumor even if it is deep within the body. Conventional x rays are often used for initial evaluation, because they are relatively cheap, painless, and easily accessible. In order to increase the information obtained from a conventional x ray, air or contrast media (such as barium or iodine) may be used to enhance the images.

The most definitive diagnostic test for cancer is a biopsy, which is the surgical removal of a piece of suspect tissue for staining and microscope examination (cytochemistry). By examining certain cell characteristics, abnormalities can be identified and the presence of specific types of cells can be diagnostic for certain cancers. The biopsy provides information about the type of cancer, its stage, the aggressiveness of the cancer in invading nearby tissue or organs, and the extent of metastases at diagnosis. The pathologist who evaluates cancer cells in biopsied tissue designates the cancer as being stage I, II, III, or IV, in terms of the degree of metastasis.

Newer molecular and cellular diagnostic testing, such as polymerase chain reaction (PCR), allows the molecular genetic analysis of tumors. Cytogenetic analysis of tumor chromosomes, for example, can identify structural abnormalities that may explain the unique origins of cancer in an individual child. Spectral karyotyping (SKY), an advanced method of screening chromosomes for numeric and structural abnormalities, is used to evaluate pediatric tumors. Gene sequences can also be evaluated in a method (comparative genomic hybridization) that compares samples from a tumor and normal tissue after both have been exposed to the same radioactive material. This method can determine gains and losses in DNA in the region of the tumor, detecting alterations that have caused the cancer. The developing science of proteomics studies specific proteins in cells and may someday be able to provide detailed assessment of cancer cells.

Treatment

The aim of cancer treatment is to remove or destroy all or as much of the primary tumor as possible and to prevent its recurrence or metastases. While devising a treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is highly aggressive and cure is not likely, treatment will be aimed at relieving symptoms and controlling the cancer for as long as possible.

Cancer treatment is always tailored to the individual. The treatment choice depends on the type and location of cancer, the extent to which it has already spread, and the age, sex, and general health status of the individual. The major types of treatment are: surgery, radiation, chemotherapy , immunotherapy, hormone therapy, and bone-marrow transplantation.

Advances in molecular biology and cancer genetics have contributed greatly to the development of therapies that provide cell-targeted treatment. Genetic testing uses molecular probes to identify gene mutations that have been linked to specific cancers. In the early 2000s ongoing research is focused on new treatment and prevention methods, including molecular-targeted therapies, virus therapy, immunotherapy, and drug therapy that stimulates the self-destruction of cancer cells (apoptosis).

Targeted molecular therapy, although as of 2004 still the subject of concentrated research, was being used effectively in pediatric study subjects where it has been shown to reduce the toxicity seen with conventional chemotherapy. Unlike chemotherapy, which treats all cells uniformly, targeted molecular therapy can focus on selected cells without affecting normal cells and tissues. This refinement frees children from some of the long-term toxic effects and complications that can negatively affect quality of life and survival even if the cancer is cured.

Surgery

Surgical removal of a solid tumor is most effective with small tumors confined to one area of the body. Surgery removes the tumor (tumor resection) and usually part of the surrounding tissue to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes are sometimes removed as well. Surgery may also be preventive or prophylactic, removing an abnormal looking area of tissue that is likely to become malignant over time. During surgery biopsies may also be performed on tissue that may be affected by metastases. Surgery is not a typical treatment for leukemia or lymphoma, which arise in the circulatory system and lymphatic systems that extend throughout the body. Children with osteosarcoma (bone cancer) and other solid tumors are candidates for surgery, however.

Surgery may be performed in conjunction with radiation (cytoreductive surgery) or chemotherapy. The surgeon removes as much of the cancer as possible and the remaining area is treated with radiotherapy or chemotherapy or both. In advanced metastatic cancer when cure is unlikely, palliative surgery aims at reducing symptoms. Debulking surgery, for example, removes part of a tumor that is pressing on other organs and causing pain. In tumors that are dependent on hormones, one option is to remove organs that secrete the hormones.

Radiation therapy

Radiation kills tumor cells and is used alone when a tumor is in a poor location for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. External radiation is aimed at the tumor from outside the body. In internal radiation (brachytherapy), radioactive liquid or

A transmission electron micrograph (TEM) of two spindle cell nuclei from a human sarcoma. Sarcomas are cancers of the connective tissue (bone, nerves, smooth muscle). (Photograph by Dr. Brian Eyden. National Audubon Society Collection/Photo Res
A transmission electron micrograph (TEM) of two spindle cell nuclei from a human sarcoma. Sarcomas are cancers of the connective tissue (bone, nerves, smooth muscle).
(Photograph by Dr. Brian Eyden. National Audubon Society Collection/Photo Researchers, Inc.)
pellets are delivered to the cancerous site via a pill, injection, or insertion in a sealed container.

Chemotherapy

Chemotherapy is the administration of drugs that kill cancer cells (cytotoxic drugs). It destroys hard-to-detect cancer cells that have spread (metastasized) through the circulation or lymph system. Chemotherapeutic drugs are given orally or intravenously, either alone or in conjunction with surgery, radiation, or both. When chemotherapy is used before surgery or radiation, it is known as primary chemotherapy or neoadjuvant chemotherapy. Because the cancer cells have not yet been exposed to anti-cancer drugs, they are especially vulnerable, allowing neoadjuvant therapy to effectively reduce tumor size. However, the toxic effects of neoadjuvant chemotherapy may be severe, because normal cells are also destroyed. Chemotherapy may also make the body less tolerant of the side effects of other treatments such as radiation therapy. Adjuvant therapy is the more common type of chemotherapy, used to enhance the effectiveness of other treatments.

Immunotherapy

Immunotherapy uses the body's own immune system, specifically a type of disease-fighting white cell called T-cells, to destroy cancer cells. Tumor-specific proteins that are part of unique genetic mutations in pediatric cancer, for example, are believed to be ideal targets for anti-tumor immune processes. Various immunological agents are as of 2004 still in clinical trials and are not as of that year widely available, though initial results are promising. Monoclonal antibodies are used to

(Table by GGS Information Services.)
(Table by GGS Information Services.)

Common childhood cancers
Percentage of total childhood cancers Type of cancer
SOURCE : Margo Hoover-Regan. http://www.csupomona.edu/~cancerbio/pediatric%20cancer%20-%20Dr.%20H over-Regan.htm. Updated May 15, 2000.
39% Leukemia (white blood cell cancer) and lymphoma (lymph system cancer)
20.7% Brain cancers (brain and spinal cord tumors)
7.3% Neuroblastoma (nerve cell cancer, most commonly in the adrenal gland)
6.1% Wilms' tumor (kidney cancer that can metastasize to lung)
4.7% Osteosarcoma (bone cancer) and Ewing's sarcoma (cancer in the bone shaft)
3.4% Rhabdomyosarcoma (muscle tissue cancer, most often in head and neck)
2.9% Retinoblastoma (malignant eye tumor)
16.4% Germ cell cancer (ovarian or testicular cancers) and others

fight cancer cells in much the same way as antibodies that are produced by the body's own immune system work to fight infection. Other substances are also being used experimentally. They include substances such as interferons, interleukins, growth factors, monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer but are designed to treat existing disease. They work by boosting the immune system and training immunized cells to destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for cancers that are hormone-dependent and grow faster in the presence of specific hormones, such as cancer of the prostate, breast, and uterus. Hormone therapy blocks the production or action of these hormones, slowing growth of the tumor and extending survival for months or years.

Bone marrow transplantation

Bone marrow is the tissue within bone cavities that produces blood cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes drugs or radiation needed to destroy cancer cells also destroys bone marrow and only replacement with healthy cells counteracts this adverse effect. A bone marrow transplant involves removing marrow from a donor and transplanting blood-forming cells to a recipient. While not a therapy in itself, bone marrow transplantation may allow a cancer patient to undergo aggressive therapy.

Many specialists work together to treat cancer patients. The oncologist is a physician who specializes in cancer care and usually coordinates the treatment plan, directing chemotherapy, hormone therapy, and any treatment that does not involve radiation or surgery. The radiation oncologist uses radiation to treat cancer, while the surgical oncologist performs surgery to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians who treat women's and children's cancers. Radiologists read the x rays, ultrasound images, CT scans, and MRI images to help diagnose cancer. Hematologists specialize in disorders of the blood and bone marrow and are consulted in the evaluation of leukemia, lymphoma, and bone cancer.

Alternative treatment

A range of alternative treatments are available to help treat cancer that can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation. Alternative treatment of cancer is a complicated arena and a trained complementary health practitioner should be consulted.

Although the effectiveness of complementary therapies such as acupuncture in alleviating cancer pain have not as of 2004 been clinically proven, many cancer patients find it safe and beneficial. Bodywork therapies such as massage and reflexology ease muscle tension and may alleviate side effects such as nausea and vomiting . Homeopathy and herbal remedies used in Chinese traditional herbal medicine also have been shown to alleviate some of the side effects of radiation and chemotherapy and are being recommended by many doctors.

Prognosis

Most cancers show good cure rates if detected and treated at early stages. The prognosis involves the type of cancer, its degree of invasiveness, and the extent of metastases at diagnosis. In addition, age, general health status, and response to treatment are important factors. Cancer deaths in children have shown consistent declines, decreasing between 1975 and 2000 from 50 in 1 million diagnosed to 25 in 1 million. However, cancer is the leading cause of death among children and adolescents, responsible for 2,700 deaths each year in the United States.

Prevention

Prevention of cancer means being aware of causes and risks, which involve a combination of genetic and environmental factors. Except for family history, specific genetic causes or an inherited predisposition are generally unknown in individuals until revealed in the diagnostic process. Known environmental causes can be avoided, however. A list of guidelines offered by nutritionists and epidemiologists from leading U.S. universities to reduce the risk of cancer includes some that may apply to children and adolescents:

  • Eat plenty of vegetables and fruits, especially cruciferous vegetables such as broccoli, cauliflower, and cabbage.
  • Decrease or avoid eating animal fats and red meats.
  • Exercise vigorously for at least 20 minutes every day.
  • Avoid excessive weight gain.
  • Avoid tobacco (including second hand smoke).
  • Avoid excessive amounts of alcohol.
  • Avoid midday sun (between 11 a.m. and 3 p.m.) when rays are the strongest.
  • Avoid risky sexual practices and multiple partners.
  • Avoid known carcinogens in the environment or work place.

Certain drugs being used as of 2004 for treatment could also be suitable for prevention, at least prevention of recurrences. For example, the drug tamoxifen has been very effective against breast cancer and is in 2004 being used to prevent recurrence in breast cancer survivors. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression of or to prevent head and neck cancers. Certain studies suggest that cancer incidence is lower in areas where soil and foods are rich in the mineral selenium.

Nutritional concerns

Certain foods, including many vegetables, fruits, and grains, are believed to offer protection against various cancers. In laboratory studies, vitamins such as A, C, and E, as well as beta-carotene found in carrots and isothiocyanate and dithiolthione compounds found in cruciferous vegetables, such as broccoli, cauliflower, and cabbage, have been shown to provide protection against certain types of cancer. Studies have shown that eating a diet rich in fiber as found in fruits, vegetables, and whole grains can reduce the risk of colon cancer.

KEY TERMS

Benign —In medical usage, benign is the opposite of malignant. It describes an abnormal growth that is stable, treatable, and generally not life-threatening.

Biopsy —The surgical removal and microscopic examination of living tissue for diagnostic purposes or to follow the course of a disease. Most commonly the term refers to the collection and analysis of tissue from a suspected tumor to establish malignancy.

Bone marrow —The spongy tissue inside the large bones in the body that is responsible for making the red blood cells, most white blood cells, and platelets.

Carcinogenic —A substance that can cause cancer to develop.

Chemotherapy —Any treatment of an illness with chemical agents. The term is usually used to describe the treatment of cancer with drugs that inhibit cancer growth or destroy cancer cells.

Epithelium —The layer of cells that covers body surfaces, lines body cavities, and forms glands.

Hormone therapy —Treating cancers by changing the hormone balance of the body, instead of by using cell-killing drugs.

Immunotherapy —A mode of cancer treatment in which the immune system is stimulated to fight the cancer.

Malignant —Cells that have been altered such that they have lost normal control mechanisms and are capable of local invasion and spread to other areas of the body. Often used to describe a cancer.

Metastasis —A secondary tumor resulting from the spread of cancerous cells from the primary tumor to other parts of the body.

Radiation therapy —A cancer treatment that uses high-energy rays or particles to kill or weaken cancer cells. Radiation may be delivered externally or internally via surgically implanted pellets. Also called radiotherapy.

Sore —A wound, lesion, or ulcer on the skin.

Tumor —A growth of tissue resulting from the uncontrolled proliferation of cells.

Parental concerns

A diagnosis of childhood cancer raises many uncertainties and concerns for parents, including how to acquire the most effective therapy. Advances in molecular and cellular technologies have improved both the diagnosis and treatment of pediatric cancer and also carry with them the possibility of someday curing and preventing cancer in children. While cancer was at one time nearly always fatal in children, as of 2004 more than 75 percent of children diagnosed with cancer enjoyed disease-free survival. Targeted molecular therapy and immunotherapies are the ongoing focus of concentrated research, and studies using these cell-selective technologies in treating children have shown encouraging results, both in earlier responses and reduced toxicity and complications longer term. Parents can be assured of access to the current knowledge base in molecular biology and advanced treatment technologies that promise better outcomes.

See also Leukemias, acute ; Leukemias, chronic .

Resources

BOOKS

Janes-Hodder, Honna, et al. Childhood Cancer: A Parent's Guide to Solid Tumor Cancers , 2nd ed. Cambridge, MA: O'Reilly Media Inc., 2002.

Woznick, Leigh A., and Carol D. Goodheart. Living with Childhood Cancer: A Practical Guide to Help Families Cope. Washington, DC: American Psychological Association (APA), 2002.

ORGANIZATIONS

American Cancer Society. 1599 Clifton Road, NE, Atlanta, GA 30329. Web site: http://www.cancer.org.

Cancer Research Institute (National Headquarters). 681 Fifth Avenue, New York, NY 10022. Web site: http://www.cancerresearch.org.

National Cancer Institute. 9000 Rockville Pike, Building 31, room 10A16, Bethesda, MD 20892. Web site: http://wwwicic.nci.nih.gov.

National Children's Cancer Society. 1015 Locust Suite 600, St. Louis, MO 63101. Web site: http://www.nationalchildrenscancersociety.com.

WEB SITES

"Childhood Cancer." Kid's Health , 2004. Available online at http://www.kidshealth.org/parent/medical/cancer/cancer.html (accessed December 8, 2004).

L. Lee Culvert Rosalyn Carson-DeWitt, MD Teresa G. Odle



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