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Cancer is a group of diseases characterized by uncontrolled cell division leading to growth of abnormal tissue. It is believed that cancers arise from both genetic and environmental factors that lead to aberrant growth regulation of a stem cell population, or by the dedifferentiation of more mature cell types.
Cell multiplication (proliferation) is a normal physiologic process that occurs in almost all tissues and under many circumstances, such as response to injury, immune responses, or to replace cells that have died or have been shed as a part of their lifecycle (in tissues such as skin or the mucous membranes of the digestive tract). Normally the balance between proliferation and cell death is tightly regulated to ensure the integrity of organs and tissues. Mutations in DNA that lead to cancer appear to disrupt these orderly processes.
The uncontrolled and often rapid proliferation of cells can lead to either a benign tumor or a malignant tumor (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life. Malignant tumors can invade other organs, spread to distant locations (metastasize) and become life threatening.
Signs and symptoms
While advanced cancer may cause pain, it is not always the first symptom. Roughly, cancer symptoms can be divided into three groups:
Local symptoms: unusual swelling (tumor in Latin means swelling), hemorrhage (bleeding), ulceration or jaundice.
Symptoms of metastasis (spreading): enlarged lymph nodes, cough and hemoptysis, hepatomegaly (enlarged liver), bone pain, fracture of affected bones and neurological symptoms.
Systemic symptoms: weight loss, poor appetite and cachexia, excessive sweating (night sweats), anemia, and specific paraneoplastic phenomena, i.e. specific conditions that are due to an active cancer, such as thrombosis or hormonal changes.
Every single item in the above list has a substantial differential diagnosis (it may be associated with unrelated diseases). Often, cancer is an unexpected finding during investigation for much more common symptoms, while others are diagnosed through screening (see below).
Types of cancer
Cancers originate within a single cell. Hence, cancers can be classified by the type of cell in which it originates and by the location of the cell.
Carcinomas originate in epithelial cells, e.g. skin, digestive tract or glands. Leukemia starts in the bone marrow stem cells. Lymphoma is a cancer originating in lymphatic tissue. Melanoma arises in melanocytes. Sarcoma begins in the connective tissue of bone or muscle. Teratoma begins within germ cells.
Adult cancers
Adult cancers usually form in epithelial tissues and are believed often to be the result of a long biological process related to the interaction of exogenous exposures with genetic and other endogenous characteristics among susceptible people. Examples include: bladder carcinoma, blood (and bone marrow) - hematological malignancies, leukemia, lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma, brain tumor, breast cancer, cervical cancer, colorectal cancer - in the colon, rectum, anus, or appendix, esophageal cancer, endometrial cancer - in the uterus, hepatocellular carcinoma - in the liver, gastrointestinal stromal tumor (GIST), laryngeal cancer, lung cancer, mesothelioma - in the pleura or pericardium, oral cancer, osteosarcoma - in bones, ovarian cancer, pancreatic cancer, prostate cancer, renal cell carcinoma - in the kidneys, rhabdomyosarcoma - in muscles, skin cancer (including benign moles and dysplastic nevi), stomach cancer, testicular cancer, and thyroid cancer.
Childhood cancers
Cancer can also occur in young children, particularly infants. Here, the aberrant genetic processes that fail to safeguard against the clonal proliferation of cells with unregulated growth potential occur very early in life and progress very quickly.
The age of peak incidence of cancer in children occurs during the first year of life. Neuroblastoma is the most common infant malignancy, followed by the leukemias and the central nervous system cancers. Female infants and male infants have essentially the same overall cancer incidence rates, but white infants have substantially higher cancer rates than black infants for most cancer types. Relative survival for infants is very good for neuroblastoma, Wilms' tumor and retinoblastoma, but not for most other types of cancer. Childhood cancers include, from most frequently occurring to least: Neuroblastoma, leukemia, central nervous system, retinoblastoma, Wilms' tumor, germ cell, soft tissue sarcomas, hepatic, lymphomas (such as Hodgkin's disease), epithelial.
Diagnosing cancer
Biopsy
A biopsy leads to the definitive diagnosis of most malignancies. It requires the removal of cells and/or pieces of tissue for examination by a pathologist. The tissue diagnosis indicates the type of cell that is proliferating, its severity (degree of dysplasia), its extent and size, and - sometimes with help from cytogenetics and immunohistochemistry - prognostic and therapeutic determinants.
Biopsy can be curative if the whole lesion is removed; in this case, the borders of the sample are examined closely to see if all malignant tissue has truly been excised.
The nature of the biopsy depends on the organ that is sampled. Many biopsies (such as those of the skin, breast or liver) can happen on an outpatient basis. Biopsies of other organs are performed under anesthesia and require surgery.
Screening
Cancer screening is the widespread uses of tests to detect cancers in the population. It is often an inexpensive, noninvasive procedure. If signs of cancer are detected, more definitive and invasive followup tests are performed to confirm the diagnosis.
Screening for cancer can lead to earlier diagnosis. Early diagnosis may lead to extended life. A number of different screening tests have been developed. Colon cancer can be detected through fecal occult blood testing and colonoscopy, which reduces both colon cancer incidence and mortality, presumably through the detection and removal of precancerous polyps. Similarly, cervical cytology testing (using the Pap smear) leads to the identification and excision of precancerous lesions. Over time, such testing has been followed by a dramatic reduction of cervical cancer incidence and mortality. Breast cancers can be detected by breast self-examination and regular screening mammograms. Testicular self-examination – is recommended for men from the age of 15 years to detect testicular cancer. Prostate cancer can be screened for by a digital rectal exam along with annual prostate specific antigen blood testing.
Screening for cancer is controversial in cases when it is not yet known if this test actually saves lives. The controversy arises when it is not clear if the benefits of screening outweigh the risks of follow-up diagnostic tests and cancer treatments. For example: when screening for prostate cancer, the PSA test may detect small cancers that would never become life threatening, but once detected will lead to treatment. This situation, called overdiagnosis, puts men at risk for complications from unnecessary treatment such as surgery or radiation. Followup procedures used to diagnose prostate cancer (prostate biopsy) may cause side effects, including bleeding and infection. Prostate cancer treatment may cause incontinence (inability to control urine flow) and erectile dysfunction (erections inadequate for intercourse). For these reasons, it is important that the benefits and risks of diagnostic procedures and treatment be taken into account when considering whether to undertake cancer screening.
Use of medical imaging to search for cancer in people without clear symptoms is similarly marred with problems. There is a significant risk of detection of an incidentaloma - a benign lesion that may be interpreted as a malignancy and be subjected to potentially dangerous investigations.
Treatment of cancer
Cancer can be treated by surgery, chemotherapy, radiation therapy or other methods. The choice of therapy depends upon the location and grade of the tumor and the stage of the disease.
Surgery
If the tumor is localized, surgery is often the preferred treatment. Example procedures include prostatectomy for prostate cancer and mastectomy for breast cancer. The goal of the surgery can be either the removal of only the tumor, or the entire organ. Since a single cancer cell can grow into a sizeable tumor, removing only the tumor leads to a greater chance of recurrence. A margin of healthy tissue is often resected to allow for small amounts of residual tumor cells.
In addition to removal of the primary tumor, surgery is often necessary for staging, e.g. determining the extent of the disease and whether there has been metastasis to regional lymph nodes. Staging determines the prognosis and the need for adjuvant therapy.
Chemotherapy
Chemotherapy is the treatment of cancer with drugs that can destroy cancer cells. These drugs often are called "anticancer" drugs. Normal cells grow and die in a controlled way. When cancer occurs, cells in the body that are not normal keep dividing and forming more cells without control. Anticancer drugs destroy cancer cells by stopping them from growing or multiplying. Healthy cells can also be harmed, especially those that divide quickly. Harm to healthy cells is what causes side effects. These cells usually repair themselves after chemotherapy. Because some drugs work better together than alone, two or more drugs are often given at the same time. This is called combination chemotherapy.
Radiation therapy
Radiation therapy (also called radiotherapy, x-ray therapy, or irradiation) is the use of a certain type of energy (called ionizing radiation) to kill cancer cells and shrink tumors. Radiation therapy injures or destroys cells in the area being treated (the "target tissue") by damaging their genetic material, making it impossible for these cells to continue to grow and divide. Although radiation damages both cancer cells and normal cells, most normal cells can recover from the effects of radiation and function properly. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue.
Radiation therapy may be used to treat almost every type of solid tumor, including cancers of the brain, breast, cervix, larynx, lung, pancreas, prostate, skin, spine, stomach, uterus, or soft tissue sarcomas. Radiation can also be used to treat leukemia and lymphoma (cancers of the blood-forming cells and lymphatic system, respectively). Radiation dose to each site depends on a number of factors, including the type of cancer and whether there are tissues and organs nearby that may be damaged by radiation.
Clinical trials
Clinical trials, also called experimental cancer treatment or research studies, test new treatments in people with cancer. The goal of this research is to find better ways to treat cancer and help cancer patients. Clinical trials test many types of treatment such as new drugs, new approaches to surgery or radiation therapy, new combinations of treatments, or new methods such as gene therapy.
A clinical trial is one of the final stages of a long and careful cancer research process. The search for new treatments begins in the laboratory, where scientists first develop and test new ideas. If an approach seems promising, the next step may be testing a treatment in animals to see how it affects cancer in a living being and whether it has harmful effects. Of course, treatments that work well in the lab or in animals do not always work well in people. Studies are done with cancer patients to find out whether promising treatments are safe and effective.
The patients who take part may be helped personally by the treatment(s) they receive. They get up-to-date care from cancer experts, and they receive either a new treatment being tested or the best available standard treatment for their cancer. Of course, there is no guarantee that a new treatment being tested or a standard treatment will produce good results. New treatments also may have unknown risks. But if a new treatment proves effective or more effective than standard treatment, study patients who receive it may be among the first to benefit. Some patients receive only standard treatment and benefit from it.
Complementary and alternative medicine
Complementary and alternative medicine (CAM) is a group of diverse medical and health care systems, practices, and products that are not presently considered to be part of conventional medicine. It is important that the same scientific evaluation that is used to assess conventional approaches can be used to evaluate CAM therapies. In the United States, current trials are underway to test the following:
acupuncture to reduce the symptoms of advanced colorectal cancer,
combination chemotherapy plus radiation therapy with or without shark cartilage in the treatment of patients who have non-small cell lung cancer that cannot be removed by surgery,
hyperbaric oxygen therapy with laryngectomy patients (people who have had an operation to remove all or part of the larynx (voice box)),
massage therapy for cancer-related fatigue,
chemotherapy compared with pancreatic enzyme therapy plus specialized diet for the treatment of pancreatic cancer, and
mistletoe extract and chemotherapy for the treatment of solid tumors.
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This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "Cancer"
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