Cancerous tumor

Definition of Cancerous Tumor by Medical dictionary


Definition

Cancer is not just one disease, but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death.

Description

One out of every four deaths in the United States is from cancer. It is second only to heart disease as a cause of death in the states. About 1.2 million Americans are diagnosed with cancer annually; more than 500,000 die of cancer annually.
Cancer can attack anyone. Since the occurrence of cancer increases as individuals age, most of the cases are seen in adults, middle-aged or older. Sixty percent of all cancers are diagnosed in people who are older than 65 years of age. The most common cancers are skin cancer, lung cancer, colon cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.
Cancer, by definition, is a disease of the genes. A gene is a small part of DNA, which is the master molecule of the cell. Genes make “proteins,” which are the ultimate workhorses of the cells. It is these proteins that allow our bodies to carry out all the many processes that permit us to breathe, think, move, etc.
Throughout people’s lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose its restraints on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a “tumor” or neoplasm (medical term for cancer meaning “new growth”).
In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some mutant cells may escape immune detection and survive to become tumors or cancers.
Tumors are of two types, benign or malignant. A benign tumor is not considered cancer. It is slow growing, does not spread or invade surrounding tissue, and once it is removed, doesn’t usually recur. A malignant tumor, on the other hand, is cancer. It invades surrounding tissue and spreads to other parts of the body. If the cancer cells have spread to the surrounding tissues, even after the malignant tumor is removed, it generally recurs.
A majority of cancers are caused by changes in the cell’s DNA because of damage due to the environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens, and there are many types.
There are some cancers that have a genetic basis. In other words, an individual could inherit faulty DNA from his parents, which could predispose him to getting cancer. While there is scientific evidence that both factors (environmental and genetic) play a role, less than 10% of all cancers are purely hereditary. Cancers that are known to have a hereditary link are breast cancer, colon cancer, ovarian cancer, and uterine cancer. Besides genes, certain physiological traits could be inherited and could contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer, but only if he or she also has prolonged exposure to intensive sunlight.
There are several different types of cancers:
  • Carcinomas are cancers that arise in the epithelium (the layer of cells covering the body’s surface and lining the internal organs and various glands). Ninety percent of human cancers fall into this category. Carcinomas can be subdivided into two types: adenocarcinomas and squamous cell carcinomas. Adenocarcinomas are cancers that develop in an organ or a gland, while squamous cell carcinomas refer to cancers that originate in the skin.
  • Melanomas also originate in the skin, usually in the pigment cells (melanocytes).
  • Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle and blood vessels.
  • Cancers of the blood and lymph glands are called leukemias and lymphomas respectively.
  • Gliomas are cancers of the nerve tissue.

Causes and symptoms

The major risk factors for cancer are: tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment and pollution.
According to estimates of the American Cancer Society (ACS), approximately 40% of cancer deaths in 1998 were due to tobacco and excessive alcohol use. An additional one-third of the deaths were related to diet and nutrition. Many of the one million skin cancers diagnosed in 1998 were due to over-exposure to ultraviolet light from the sun’s rays.
Frequency Of Cancer-Related Death
Cancer Site Number of Deaths Per Year
Lung 160,100
Colon and rectum 56,500
Breast 43,900
Prostate 39,200
Pancreas 28,900
Lymphoma 26,300
Leukemia 21,600
Brain 17,400
Stomach 13,700
Liver 13,000
Esophagus 11,900
Bladder 12,500
Kidney 11,600
Multiple myeloma 11,300

Tobacco

Eighty to 90% of lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of upper respiratory tract, esophagus, larynx, bladder, pancreas, and probably liver, stomach, breast, and kidney as well. Recently, scientists have also shown that second-hand smoke (or passive smoking) can increase one’s risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers, such as liver cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers.

Diet

Thirty-five percent of all cancers are due to dietary causes. Excessive intake of fat leading to obesity has been associated with cancers of the breast, colon, rectum, pancreas, prostate, gall bladder, ovaries, and uterus.

Sexual and reproductive behavior

The human papillomavirus, which is sexually transmitted, has been shown to cause cancer of the cervix. Having too many sex partners and becoming sexually active early has been shown to increase one’s chances of contracting this disease. In addition, it has also been shown that women who don’t have children or have children late in life have an increased risk for both ovarian and breast cancer.

Infectious agents

In the last 20 years, scientists have obtained evidence to show that approximately 15% of the world’s cancer deaths can be traced to viruses, bacteria, or parasites. The most common cancer-causing pathogens and the cancers associated with them are shown in table form.

Family history

Certain cancers like breast, colon, ovarian, and uterine cancer recur generation after generation in some families. A few cancers, such as the eye cancer “retinoblastoma,” a type of colon cancer, and a type of breast cancer known as “early-onset breast cancer,” have been shown to be linked to certain genes that can be tracked within a family. It is therefore possible that inheriting particular genes makes a person susceptible to certain cancers.

Occupational hazards

There is evidence to prove that certain occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, a higher likelihood of getting bladder cancer is associated with dye, rubber and gas workers; skin and lung cancer with smelters, gold miners and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC manufacturers; and lung, bone and bone marrow cancer with radiologists and uranium miners.

Environment

Radiation is believed to cause 1-2% of all cancer deaths. Ultra-violet 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

Several studies have shown that there is a well-established link between asbestos and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollution occurs when dangerous chemicals from the industries escape into the surrounding environment. It has been estimated that 1% of cancer deaths are due to air, land, and water pollution.
COMMON PATHOGENS AND THE CANCERS ASSOCIATED WITH THEM
Causative Agent Type of Cancer
Viruses
Papillomaviruses Cancer of the cervix
Hepatitis B virus Liver cancer
Hepatitis C virus Liver cancer
Epstein-Barr virus Burkitt’s lymphoma
Cancers of the upper
pharynx
Hodgkin’s lymphoma, Non-Hodgkin’s
lymphoma, Gastric cancers
Human
immunodeficiency
virus (HIV)
Kaposi’s sarcoma Lymphoma
Bacteria
Helicobacter pylori Stomach cancer Lymphomas
Cancer is a progressive disease, and goes through several stages. Each stage may produce a number of symptoms. Some symptoms are produced early and may occur due to a tumor that is growing within an organ or a gland. As the tumor grows, it may press on the nearby nerves, organs, and blood vessels. This causes pain and some pressure which may be the earliest warning signs of cancer.
Despite the fact that there are several hundred different types of cancers, producing very different symptoms, the ACS 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 in swallowing
  • any change in bowel or bladder habits
Many other diseases, besides cancer, could produce the same symptoms. However, it is important to have these symptoms checked, as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers such as breast cancer may not have any early symptoms. Therefore, it is important to undergo routine screening tests such as breast self-exams and mammograms.

Diagnosis

Diagnosis begins with a thorough physical examination and a complete medical history. The doctor will observe, feel and palpate (apply pressure by touch) different parts of the body in order to identify any variations from the normal size, feel, and texture of the organ or tissue.
As part of the physical exam, the doctor will inspect the oral cavity, or the mouth. By focusing a light into the mouth, he will look for abnormalities in color, moisture, surface texture, or presence of any thickening or sore in the lips, tongue, gums, the hard palate on the roof of the mouth, and the throat. To detect thyroid cancer, the doctor will observe the front of the neck for swelling. He may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland (located at the base of the neck) to detect any nodules or tenderness. As part of the physical examination, the doctor will also palpate the lymph nodes in the neck, under the arms and in the groin. Many illnesses and cancers cause a swelling of the lymph nodes.
The doctor may conduct a thorough examination of the skin to look for sores that have been present for more than three weeks and that bleed, ooze, or crust; irritated patches that may itch or hurt, and any change in the size of a wart or a mole.
Examination of the female pelvis is used to detect cancers of the ovaries, uterus, cervix, and vagina. In the visual examination, the doctor looks for abnormal discharges or the presence of sores. Then, using gloved hands the physician palpates the internal pelvic organs such as the uterus and ovaries to detect any abnormal masses. Breast examination includes visual observation where the doctor looks for any discharge, unevenness, discoloration, or scaling. The doctor palpates both breasts to feel for masses or lumps.
For males, inspection of the rectum and the prostate is also included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for any growths, tumors, or other abnormalities. The doctor also conducts an examination of the testes, where the doctor observes the genital area and looks for swelling or other abnormalities. The testicles are palpated to identify any lumps, thickening or differences in the size, weight and firmness.
If the doctor detects an abnormality on physical examination, or the patient has some symptom that could be indicative of cancer, the doctor may order diagnostic tests.
Laboratory studies of sputum (sputum cytology), blood, urine, and stool can detect abnormalities that may indicate cancer. Sputum cytology is a test where the phlegm that is coughed up from the lungs is microscopically examined. It is often used to detect lung cancer. A blood test for cancer is easy to perform, usually inexpensive and risk-free. The blood sample is obtained by a lab technician or a doctor by inserting a needle into a vein and is relatively painless. Blood tests can be either specific or non-specific. Often, in certain cancers, the cancer cells release particular proteins (called tumor markers) and blood tests can be used to detect the presence of these tumor markers. However, with a few exceptions, tumor markers are not used for routine screening of cancers, because several non-cancerous conditions also produce positive results. Blood tests are generally more useful in monitoring the effectiveness of the treatment, or in following the course of the disease and detecting recurrent disease.
Imaging tests such as computed tomography scans (CT scans), magnetic resonance imaging (MRI), ultrasound and fiberoptic scope examinations help the doctors determine the location of the 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 a dye (such as barium or iodine) may be used as a contrast medium to outline or highlight parts of the body.
The most definitive diagnostic test is the biopsy, wherein a piece of tissue is surgically removed for microscope examination. Besides confirming a cancer, the biopsy also provides information about the type of cancer, the stage it has reached, the aggressiveness of the cancer and the extent of its spread. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests.
Screening examinations conducted regularly by healthcare professionals can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, tongue, mouth, and skin at early stages, when treatment is more likely to be successful. Some of the routine screening tests recommended by the ACS are sigmoidoscopy (for colorectal cancer), mammography (for breast cancer), pap smear (for cervical cancer), and the PSA test (for prostate cancer). Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting the tumors before the symptoms become serious.
A recent revolution in molecular biology and cancer genetics has contributed a great deal to the development of several tests designed to assess one’s risk of getting cancers. These new techniques include genetic testing, where molecular probes are used to identify mutations in certain genes that have been linked to particular cancers. At present, however, there are a lot of limitations to genetic testing and its utility appears ambiguous, emphasizing the need to develop better strategies for early detection.

Treatment

Treatment and prevention of cancers continue to be the focus of a great deal of research. In 2003, research into new cancer therapies included cancertargeting gene therapy, virus therapy, and a drug that stimulated apoptosis, or self-destruction of cancer cells, but not healthy cells. However, all of these new therapies take years of clinical testing and research.
The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. 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 very aggressive and a cure is not possible, then the treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.
Cancer treatment can take many different forms, and it is always tailored to the individual patient. The decision on which type of treatment is the most appropriate depends on the type and location of cancer, the extent to which it has already spread, the patient’s age, sex, general health status and personal treatment preferences. The major types of treatment are: surgery, radiation, chemotherapy, immunotherapy, hormone therapy, and bone-marrow transplantation.

Surgery

Surgery is the removal of a visible tumor and is the most frequently used cancer treatment. It is most effective when a cancer is small and confined to one area of the body.
Surgery can be used for many purposes.
  • Treatment. Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some part of the normal surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes may be examined and sometimes are removed as well.
  • Preventive surgery. Preventive or prophylactic surgery involves removal of an abnormal looking area that is likely to become malignant over time. For example, 40% of people with a colon disease known as ulcerative colitis, ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed and reduce the risk significantly.
  • Diagnostic purposes. The most definitive tool for diagnosing cancer is a biopsy. Sometimes, a biopsy can be performed by inserting a needle through the skin. However, at other times, the only way to obtain a tissue sample for biopsy is by performing a surgical operation.
  • Cytoreductive surgery is a procedure where the doctor removes as much of the cancer as possible, and then treats the remaining area with radiation therapy or chemotherapy or both.
  • Palliative surgery is aimed at curing the symptoms, not the cancer. Usually, in such cases, the tumor is so large or has spread so much that removing the entire tumor is not an option. For example, a tumor in the abdomen may be so large that it may press on and block a portion of the intestine, interfering with digestion and causing pain and vomiting. “Debulking surgery” may remove a part of the blockage and relieve the symptoms. In tumors that are dependent on hormones, removal of the organs that secrete the hormones is an option. For example, in prostate cancer, the release of testosterone by the testicles stimulates the growth of cancerous cells. Hence, a man may undergo an “orchiectomy” (removal of testicles) to slow the progress of the disease. Similarly, in a type of aggressive breast cancer, removal of the ovaries (oophorectomy) will stop the synthesis of hormones from the ovaries and slow the progression of the cancer.

Radiation therapy

Radiation kills tumor cells. Radiation is used alone in cases where a tumor is unsuitable for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. In the external form, the radiation is aimed at the tumor from outside the body. In internal radiation (also known as brachytherapy), a radioactive substance in the form of pellets or liquid is placed at the cancerous site by means of a pill, injection or insertion in a sealed container.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. It destroys the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapeutic drugs can be taken either orally (by mouth) or intravenously, and may be given 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.” An advantage of neoadjuvant chemotherapy is that since the cancer cells have not been exposed to anti-cancer drugs, they are especially vulnerable. It can therefore be used effectively to reduce the size of the tumor for surgery or target it for radiation. However, the toxic effects of neoadjuvant chemotherapy are severe. In addition, it may make the body less tolerant to the side effects of other treatments that follow such as radiation therapy. The more common use of chemotherapy is adjuvant therapy, which is given to enhance the effectiveness of other treatments. For example, after surgery, adjuvant chemotherapy is given to destroy any cancerous cells that still remain in the body. In 2003, a new technique was developed to streamline identification of drug compounds that are toxic to cancerous cells but not to healthy cells. The technique identified nine dugs, one of which had never before been identified for use in cancer treatment. Researchers began looking into developing the new drug for possible use.

Immunotherapy

Immunotherapy uses the body’s own immune system to destroy cancer cells. This form of treatment is being intensively studied in clinical trials and is not yet widely available to most cancer patients. The various immunological agents being tested include substances produced by the body (such as the interferons, interleukins, and growth factors), monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer. Instead, they are designed to treat people who already have the disease. Cancer vaccines work by boosting the body’s immune system and training the immune cells to specifically destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for some types of cancers that are hormone-dependent and grow faster in the presence of particular hormones. These include cancer of the prostate, breast, and uterus. Hormone therapy involves blocking the production or action of these hormones. As a result the growth of the tumor slows down and survival may be extended for several months or years.

Bone marrow transplantation

The bone marrow is the tissue within the bone cavities that contains blood-forming cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes, the amount of drugs or radiation needed to destroy cancer cells also destroys bone marrow. Replacing the bone marrow with healthy cells counteracts this adverse effect. A bone marrow transplant is the removal of marrow from one person and the transplant of the blood-forming cells either to the same person or to someone else. Bone-marrow transplantation, while not a therapy in itself, is often used to “rescue” patients, by allowing those with cancer to undergo aggressive therapy.
Many different specialists generally work together as a team to treat cancer patients. An oncologist is a physician who specializes in cancer care. The oncologist provides chemotherapy, hormone therapy, and any other non-surgical treatment that does not involve radiation. The oncologist often serves as the primary physician and coordinates the patient’s treatment plan.
The radiation oncologist specializes in using radiation to treat cancer, while the surgical oncologist performs the operations needed to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians involved with treating women’s and children’s cancers respectively. Many other specialists also may be involved in the care of a cancer patient. For example, radiologists specialize in the use of x rays, ultrasounds, CT scans, MRI imaging and other techniques that are used to diagnose cancer. Hematologists specialize in disorders of the blood and are consulted in case of blood cancers and bone marrow cancers. The samples that are removed for biopsy are sent to a laboratory, where a pathologist examines them to determine the type of cancer and extent of the disease. Only some of the specialists who are involved with cancer care have been mentioned above. There are many other specialties, and virtually any type of medical or surgical specialist may become involved with care of the cancer patient should it become necessary.

Alternative treatment

There are a multitude of alternative treatments available to help the person with cancer. They can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation therapy. Alternative treatment of cancer is a complicated arena and a trained health practitioner should be consulted.
Although the effectiveness of complementary therapies such as acupuncture in alleviating cancer pain has not 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.
Certain foods including many vegetables, fruits, and grains are believed to offer protection against various cancers. However, isolation of the individual constituent of vegetables and fruits that are anti-cancer agents has proven difficult. In laboratory studies, vitamins such as A, C and E, as well as compounds such as isothiocyanates and dithiolthiones found in broccoli, cauliflower, and cabbage, and beta-carotene found in carrots have been shown to protect against cancer. Studies have shown that eating a diet rich in fiber as found in fruits and vegetables reduces the risk of colon cancer. Exercise and a low fat diet help control weight and reduce the risk of endometrial, breast, and colon cancer.
Certain drugs, which are currently being used for treatment, could also be suitable for prevention. For example, the drug tamoxifen (Nolvadex), which has been very effective against breast cancer, is currently being tested by the National Cancer Institute for its ability to prevent cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression or prevent head and neck cancers. Certain studies have suggested that cancer incidence is lower in areas where soil and foods are rich in the mineral selenium. More trials are needed to explain these intriguing connections.

Prognosis

“Lifetime risk” is the term that cancer researchers use to refer to the probability that an individual over the course of a lifetime will develop cancer or die from it. In the United States, men have a one in two lifetime risk of developing cancer, and for women the risk is one in three. Overall, African Americans are more likely to develop cancer than whites. African Americans are also 30% more likely to die of cancer than whites.
Most cancers are curable if detected and treated at their early stages. A cancer patient’s prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized and the aggressiveness of the cancer. In addition, the patient’s age, general health status and the effectiveness of the treatment being pursued also are important factors.
To help predict the future course and outcome of the disease and the likelihood of recovery from the disease, doctors often use statistics. The five-year survival rates are the most common measures used. The number refers to the proportion of people with cancer who are expected to be alive, five years after initial diagnosis, compared with a similar population that is free of cancer. It is important to note that while statistics can give some information about the average survival experience of cancer patients in a given population, it cannot be used to indicate individual prognosis, because no two patients are exactly alike.

Prevention

According to nutritionists and epidemiologists from leading universities in the United States, a person can reduce the chances of getting cancer by following some simple guidelines:
  • eating plenty of vegetables and fruits
  • exercising vigorously for at least 20 minutes every day
  • avoiding excessive weight gain
  • avoiding tobacco (even second hand smoke)
  • decreasing or avoiding consumption of animal fats and red meats
  • avoiding excessive amounts of alcohol
  • avoiding the midday sun (between 11 A.M. and 3 P.M.) when the sun’s rays are the strongest
  • avoiding risky sexual practices
  • avoiding known carcinogens in the environment or work place
In addition, following the advice of physicians in refraining from certain activities or drugs that are proven as risk factors for certain cancers can help lower one’s risk. For instance, while physicians have long known a small increased risk for breast cancer was linked to use of HRT, a landmark study released in 2003 proved the risk was greater than thought. The Women’s Health Initiative found that even relatively short-term use of estrogen plus progestin is associated with increased risk of breast cancer, diagnosis at a more advanced stage of the disease, and a higher number of abnormal mammograms. The longer a woman used HRT, the more her risk increased.

Resources

Books

Simone, Joseph V. “Oncology: Introduction.” In Cecil Textbook of Medicine, edited by Russel L. Cecil, et al. Philadelphia: W.B. Saunders Company, 2000.

Periodicals

“HRT Linked to Higher Breast Cancer Risk, Later Diagnosis, Abnormal Mammograms.” Women’s Health Weekly July 17, 2003: 2.
“New Way to Stop Cancer Cell Growth Described.” Gene Therapy Weekly December 12, 2002: 9.
“Researchers Find New Way to Trigger Self-Destruction of Certain Cancer Cells.” Biotech Week July 16, 2003: 285.
“Technique Streamlines Search for Anticancer Drugs.” Cancer Weekly April 15, 2003: 62.
“Virus Therapy Attacks Cancer Cells.” Cancer Weekly July 29, 2003: 50.

Organizations

American Cancer Society. 1599 Clifton Road, N.E. Atlanta, GA 30329 (800) 227-2345. http://www.cancer.org.
Cancer Research Institute (National Headquarters). 681, Fifth Avenue, New York, NY 10022 (800) 992-2623. http://www.cancerresearch.org.
National Cancer Institute. 9000 Rockville Pike, Building 31, room 10A16, Bethesda, Maryland, 20892 (800) 422-6237. http://wwwicic.nci.nih.gov.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

cancer

[kan´ser]

any malignant, cellular tumor. For specific types, see under the name, such as breast cancer or lung cancer. adj., adj can´cerous.

The term cancer encompasses a group of neoplastic diseases in which there is a transformation of normal body cells into malignant ones. This probably involves some change in the genetic material of the cells, deoxyribonucleic acid (DNA). oncogenes are the genes that organisms have evolved to regulate growth and repair of tissues. They are genetic codes for the proteins that function as signals that cells send and receive to regulate proliferation. These oncogenes are the targets of carcinogens. mutation and transformation of oncogenes may permanently affect a cell’s ability to control cell growth. Damage to the cell’s genetic material may be caused by carcinogenic agents. Normal cell lines can be transformed into cancer cells by viruses, chemical carcinogens, and radiation. Transformed cell lines have the ability to develop into malignant neoplasms. Transformed cells may also be recognized by other characteristics which include altered antigenicity, diminished contact inhibition, reduced requirements for certain nutrients, and the ability to grow in suspension. The altered cells pass on inappropriate genetic information to their offspring and begin to proliferate in an abnormal and destructive way. Normally, cells reproduce regularly to replace worn-out tissues, repair injuries, and allow for growth during the developing years. After these processes have taken place, cellular reproduction stops. Clearly the body in its normal processes regulates cell growth in an orderly manner. In cancer, there is no regulation and cell reproduction and growth is disorderly. The dangers of cancer are related to this chaotic reproduction of malignant cells.

As the cancer cells continue to proliferate, the mass of abnormal tissue that they form enlarges, ulcerates, and begins to shed cells that spread the disease locally or to distant sites. This migration is called metastasis. Some cells penetrate neighboring tissues, destroying normal cells and taking their place. Others can enter the blood stream and lymphatic vessels and be carried along in the fluid to another part of the body. Another way malignancy can be spread is by entering a body cavity and coming in contact with a healthy organ; however, this is not common.

Causes. It is doubtful that one process is involved in the etiology of all cancers. The exact cause of conversion of normal cells into cancerous ones is still not completely understood. An important factor is permanent alteration in the DNA of the cell, which is passed on to subsequent generations, but we do not know what triggers the change in DNA structure and why some people succumb to a cancer and others do not. Cellular immunity undoubtedly plays some part in one’s ability to stop the growth of cancer cells; it is believed by some that most persons develop many small cancers in their lifetime but do not develop clinical signs because their defense mechanisms destroy the malignant cells and prevent their replication.

Oncologists recognize that environmental, hereditary, and biological factors all play important roles in the development of cancer (see table). Environmental causes are believed to account for at least 50 per cent and perhaps, in some types, as much as 80 per cent of all cancers. For example, cigarette smoking is directly related to approximately 90 per cent of all cases of lung cancer. Other environmental carcinogens include industrial pollutants and radiation. Among the chemical carcinogens are arsenic from mining and smelting industries; asbestos from insulation, at construction sites and power plants; benzene from oil refineries, solvents, and insecticides; and products from coal combustion in steel and petrochemical industries. Each year new products that in all probability are carcinogenic are being produced by industrial operations. A major concern is the occupational and environmental hazards these chemicals present to those who work in or live near these plants.

Radiation from prolonged exposure to the ultraviolet rays of the sun or from injudicious use of diagnostic and therapeutic procedures involving x-rays and radioactive substances is also a significant factor in the incidence of cancer, particularly that of the skin, bone marrow, and thyroid.

Hormones, especially the synthetic estrogens given to prevent spontaneous abortion, are directly related to some cancers of the female reproductive organs.

Viruses as causal agents in the development of cancer have been subjected to intensive research efforts in recent years. The epidemiologic evidence is strongest for a relationship between hepatitis B virus and hepatocellular carcinoma and between human T-lymphotropic virus (HTLV)-1 and T-cell lymphoma. Both have a geographic distribution of cancer prevalence and viral infection as well as case-by-case associations. The association between burkitt’s lymphoma and epstein-barr virus (EBV) is likewise strong, except that there seems to be a need for an associated immunodeficiency state, such as that induced by chronic malaria. Similarly, the association between EBV and high-grade lymphoma in Western countries seems to require that an immunodeficiency state be present, either congenital or induced by the human immunodeficiency virus (HIV) or a drug such as cyclosporine.

The intriguing fact has been noted that viruses are capable of introducing new genetic material into a normal cell and transforming it into a malignant one, and that cell reproduction may be altered when viruses interact with such carcinogens as chemicals and radiation. Recent studies have shown that an extracellular enzyme, reverse transcriptase, plays an important role in the transmission of genetic information to the cell and thereby facilitates the reproduction of cancer cells.

The incidence of cancer in certain populations suggests that other factors are important in its development. It is known, for example, that some families show a high incidence of malignancy among their members, but there is no definite hereditary pattern. There also is a high incidence of cancer in persons receiving drugs for immunosuppression, yet cancer itself is immunosuppressive. It is suggested that prolonged suppression of the body’s immune response may eventually impair its ability to distinguish between self and nonself and thus render it unable to destroy malignant cells. When cancer itself acts to suppress the immune response, it may be the result of an overwhelming demand on the body to destroy more foreign cells than it is prepared to cope with at any given time.

Aging is another factor to consider in development of malignancy. Although cancer can occur at any age, older persons are more susceptible, perhaps because their powers of adaptability are weakened and they have been exposed to carcinogens longer than have younger persons.

Classification. Cancers are classified on the basis of two factors: the type of tissue and the type of cell in which they arise. Using this classification system, it is possible to identify over 150 types of cancer in humans. In the classification of cancers according to the type of tissue from which they evolve, there are two main groups, sarcomas and carcinomas. Sarcomas are of mesenchymal origin and affect such tissues as the bones and muscles; they tend to grow rapidly and to be very destructive. The carcinomas are of epithelial origin and make up the great majority of the glandular cancers and cancers of the breast, stomach, uterus, skin, and tongue. Cell type affects the appearance, rate of growth, and degree of malignancy. Thus, classification of tumors according to the type of cell from which they are derived is important in deciding the course of treatment for a specific malignancy.

Staging. An approach to describing and categorizing malignant tumors has been developed by the International Union Against Cancer (UICC) and the American Joint Committee on Cancer (AJCC). It is hoped that by standardizing the classification and staging of tumors, treatment protocols can be established and end results reporting can be utilized to determine the effectiveness of the suggested treatment. Whereas classification of tumors refers to the anatomical and histological descriptions of the tumor (see above), staging refers to the extent of the tumor. The three components of the staging system are the primary tumor (T), regional nodes (N), and metastasis (M). Subscripts may be used to describe the extent to which the malignancy has increased in size, its involvement of regional nodes, and its metastatic development (see table). For example, a tumor may be described as T1N2M0. dukes’ classification is a system of staging colorectal tumors, based on the depth of invasion and degree of metastasis.

Precancers. Some potentially dangerous cancers appear first in the form of harmless changes in the body’s tissues. The danger lies in the fact that such changes have a tendency to become malignant; hence they are known as precancers. Among them are sores that appear as thickened white patches (leukoplakia) in the mouth and on the vulva, some moles, and any chronically irritated area on the skin or the mucous membranes of the mouth and tongue. polyps are also possible precancers.

Prevention. Because environmental conditions play an important role in the etiology of many cancers, prevention is aimed at identifying carcinogens, educating the general public about them, and encouraging their avoidance. Equally important, if not more so, is recognition of causative factors related to life style and personal habits. Perhaps the best example of this is the relationship between smoking and lung cancer. When heavy consumption of alcohol is combined with cigarette smoking, the risk for cancer of the larynx, esophagus, and mouth is greatly increased.

Nutritional balance is also important in the prevention of cancer. Certain foods and food additives contain specific carcinogenic agents. Nutritional deficiency can lower resistance and increase the risk of certain types of cancers. The decrease in incidence of stomach cancer in most Western countries may possibly be the result of an increase in consumption of fruits and vegetables, since vitamin B12 deficiency (pernicious anemia) is known to be related to increased incidence of stomach cancer.

Studies have shown that a relationship exists between obesity and cancer, and between dietary excess, particularly consumption of large amounts of fats, and certain types of cancers. In general, overweight women are at increased risk for cancer of the endometrium, gallbladder, and kidney. Cancers associated with a high dietary intake of fat, with or without obesity, are those affecting the breast, ovary, endometrium, prostate, colon, and pancreas. Although neither saturated nor unsaturated fats are themselves carcinogenic, they act on the endocrine system and affect hormonal activity. The relationship of fat consumption to colon cancer is thought to be due to the effect of bile acids and their metabolites, which have been shown to act as tumor promoters in laboratory animals. In humans, patients with cancer of the colon typically have elevated levels of bile acid metabolites. Studies of various populations throughout the world have shown that bowel cancer is more prevalent among groups who eat large amounts of fat and very little food fiber. Hence the American Cancer Society recommends a low fat, high fiber diet for Americans.

The judicious use of hormones for therapeutic purposes also can reduce the incidence of some cancers. The widespread use of diethylstilbestrol (DES) to prevent threatened or habitual abortion and premature labor, beginning in the 1940s, eventually resulted in development of vaginal and cervical cancer in a significant number of the female offspring of women who took the drug while pregnant. As was previously mentioned, estrogens prescribed for relief of menopausal symptoms have been implicated in cancer in women. It is recommended that the lowest possible therapeutic dose be given to relieve the symptoms of menopause and prevent osteoporosis.

Cancer of the skin and malignant melanoma are related to prolonged exposure to the ultraviolet radiation in sunlight. The incidence of cancer of the skin is increasing in those persons who value a deep suntan and spend a significant amount of time engaged in outdoor leisure activities. Also at risk are those whose work requires that they be exposed to sunlight for prolonged periods of time, such as farmers.

Since most occupational cancers are preventable, increased awareness on the part of industry and the provision of a safe workplace environment can decrease the incidence of many kinds of cancer. It is also necessary for workers to cooperate with management in reducing exposure to carcinogens by complying with rules for preventive measures.

Ultimately, the prevention of cancer depends upon knowledge of each person’s risk factors for development of cancer, and that person’s decision to avoid whenever possible those habits and practices that predispose to the disease. There also should be frequent examination and monitoring of those who are known to be at greater risk.

Detection. In addition to routine cancer-related checkups by a health care provider for early detection of cancer, self-examination and awareness of the early danger signs of cancer are suggested as means by which lay persons can participate in detecting it in its earliest stages.

Monthly self-examination of the breast is advocated for all adult women, including those who are postmenopausal. Monthly self-examination of the testes is recommended for all males, particularly those in the age group most at risk for testicular cancer, that is, between the ages of 15 and 34 years.

Another self-administered screening technique is the test for occult blood, a symptom of colorectal cancer. This requires only that a smear of fecal material be applied to a slide, which is sent to a clinical laboratory for examination. To avoid a false positive reading, the person participating in the test is given instructions regarding ingestion of meat and other foods that could interfere with accurate test findings.

Signs of Cancer. There are seven early warning signs of cancer (see table). These signs do not necessarily signify cancer, but should they occur, a health care provider should be consulted and an examination is advisable. Other signs and symptoms depend on location and type of malignancy present.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
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Focused ultrasound therapy uses ultrasound waves to guide the application of focused, high-intensity ultrasound waves through the skin down to the target tissue.

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