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.
Showing posts with label Cancer Cause. Show all posts
Showing posts with label Cancer Cause. Show all posts
Inheriting Damaged 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.
Posted In
Cancer Cause
|
|
Genes Damaged by Substances in The Environment
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.
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.
Posted In
Cancer Cause
|
|
Three Classes of 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.
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.
Posted In
Cancer Cause
|
|
Subscribe to:
Posts (Atom)
