Mutations of these genes result in the genetic instability (increased mutability) and uninhibited growth seen in the progressive stage of cancer. The mutated genes are called oncogenes. The normal (pre-mutation) regulatory genes from which they are mutated are called proto-oncogenes. It seems somewhat bizarre to describe normal regulatory genes by referring to them as "pre-diseased but these genes were discovered by cancer researchers. Developmental biologists had no say in the matter. Oncogenes (and their corresponding proto-oncogenes) are often named by lower-case Three letter Acronyms (TLAs) that refer to their tissue and/or cancer-causing virus of discovery. For example, the ras oncogene was found in the ra t s arcoma virus.
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Cancers most vulnerable to essay radiation chemotherapy are the cancers with the highest percentage of cells undergoing division at any one time. Side-effect damage is greatest to male normal cells that divide rapidly, including blood stem cells, making patients vulnerable to anemia infection. Patients receiving intensive cancer chemotherapy more often die of infection than of cancer. The risk of developing leukemia secondary to radiation therapy is less than 1 per year subsequent to the therapy. For those who do develop leukemia after radiation therapy, the median time to appearance is ten years. Tamoxifen is an anti-estrogen used as breast cancer therapy, having the side effects of amenorrhea hot flashes. Many cancer chemotherapeutic agents have toxic effects on hair follicles, resulting in hair loss that is only partially temporary insofar as hair rarely regrows to full normalcy. Yet despite all the hazards of chemotherapy radiation treatment, there is a reasonable chance of eradicating the cancer, surviving and eventually recovering from the side effects. Cancers in advanced stages which are described as curable by chemotherapy include testicular cancer, small-cell cancer of the lung, and many forms of leukemia lymphoma. (return to contents) iii-a. Oncogenes and Tumor-Suppressor Genes in Progression Stage Of the 30,000 genes in the human genome coding for different proteins, a few hundred genes regulate growth.
(Although fewer than one in two-thousand tumor cells in the blood stream succeed in creating a new colony.) Cancer cells encourage the growth of new blood vessels to nurture their cancerous offspring. The immune system is a powerful defense against cancer, indicated by the fact that patients taking immune-suppressant drugs for a heart or kidney transplant are five times more likely to develop cancer. Cancer cells displaying abnormal proteins on their cell surface are targets of the immune system. Cancer cells that rid themselves of cell-surface proteins may lose major histocompatibility antigens, making them targets for natural killer cells, which seek-out cells lacking surface proteins. Nonetheless, book cancer cells do mutate in ways that elude the immune system. Most solid tumors can be fully cured only by surgical removal prior to malignant spreading. Malignant cancer can only be treated by agents similar to those that initiate cancer in the first place: dna-damaging radiation chemicals. These agents cause the greatest damage to cells that are reproducing most rapidly — the cancer cells.
Bones lungs are primary targets for cancers originating in other organs. An estimated 6-10 mutations are necessary for cells to transform to malignant cancer, which is why a high tendency to form mutations is important for the progression stage. Cancer database cells reduce dna repair and reduce cellular defenses against dna damage. Cancer cells transform cell signalling systems so summary as to behave as if being constantly stimulated by growth factors. Cancer cells often "immortalize losing the tendency to become senescent on repeated divisions. Cancer cells develop enzymes that degrade barrier membranes connective tissue. Cancer cells alter cell surface proteins so as to evade the immune system. Cancer cells acquire motility and the ability to implant into other tissues.
Normal cells are "good neighbors which chemically communicate with each other whether to remain static contact inhibition or to grow multiply (in response to growth factors ). Trauma or loss of cell tissue can accelerate cell growth to replace damaged or lost cell tissue. Induction of cell division ( mitogenesis ) increases mutation because dna that is replicating is more vulnerable to dna damage, and because damaged dna may be replicated before dna-repair enzymes can repair. Thus promoters are irritating or damaging substances that indirectly foster mutation as a result of chronic mitogenesis. An example of this can be seen in the fact that 80 of cases of gallbladder cancer occur in patients with gallstones. Malignant cancers spread preferentially from one organ to another. Cancer of the lung commonly spreads to the brain, cancer of the breast spreads to the adrenal glands lymph nodes, cancer of the colon spreads to the liver and cancer of the prostate spreads to the vertebrae.
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Such agents include sex hormones, growth hormone and growth factors (including Interleukin-2, secreted by helper T-cells). At high doses polycyclic hydrocarbons are essays promoters as well as initiators, by causing enough dna damage to result in necrotic cell death and consequent proliferation (cell reproduction) to restore the damaged tissues. Cell proliferation also occurs in wound healing and chronic inflammation, which is why tissue irritants act as promoters. Agents that encourage progression to malignancy are those that cause dna instability. Although most mutations are fatal to cells, a large number of mutations in a large number of cells in a benign tumor has a good chance of producing a few malignant cells. The susceptibility of different cells, tissues and organs to cancer — and the different manifestations of cancer in different cells, tissues and organs — can be so great that organ-specific cancers have been viewed as completely distinct disease conditions.
Mutation (initiation progression) occurs most readily in rapidly dividing cells, and promotion is unlikely to occur in cells that normally do not svu divide. For these reasons, cancer is rare in muscle and neurons, wherein cell division is infrequent in adult tissue. Most cancers occur in rapidly dividing cells, namely epithelial stem cells (like skin) or blood stem cells. Cancers also occur most frequently in tissues that interface between the body and the environment (skin, lung and digestive tract). Different organs are subjected to different physical cancer-causing agents. The skin is subjected to ultraviolet light, the lungs are subjected to smoke and the stomach is subjected to burnt, fatty foods. Because cells in different tissues are differentiated differently, different portions of dna are exposed to the cancer-causing agents.
In fact, the term cancer is typically restricted to refer only to malignant tumors. The Greek physician Hippocrates (400. C.) named cancer using the Greek word karkinos (crab) because of the creeping, clutching crab-claw appearance of cancerous tissue spreading into other tissue areas. Methods of categorizing the development of cancer are called staging. The development of a cancer malignancy occurs in three stages: Initiation — mutation of a single cell Promotion — reproduction of the mutant into many cells (a tumor) with the same mutation Progression — additional mutations in the tumor resulting in malignancy a single cancerous. A mutated cell could be shed away (like a skin cell be killed by the immune system or commit suicide.
Even if the mutated cell survives, it will not get beyond the initiation stage if it does not reproduce. However, a single mutated cell may survive for years or decades until some stimulus (a promoter) causes it to reproduce. But if further mutations do not occur to increase survival, reproduction the ability to spread, the tumor will remain benign and not go beyond the promotion stage. (There is, however, no benign form of leukemia.) Although cancer is a disease of mutation (dna damage) almost all cancers are due to environmental factors rather than heredity. Radiation and viruses can mutate dna, but the predominant initiators of cancer are chemical agents such as aflatoxin, reactive oxygen Species ( ros, free radicals ) and the polycyclic hydrocarbons found in tobacco smoke and broiled or smoked meat. (Other fried or broiled foods have carcinogens as well, but meats require the most cooking time and have more opportunity to burn.) Promoters are agents that encourage cell reproduction growth.
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Cancer cells are cells that have reduced their performance of specialized functions and which function more to consume resources of the body while reproducing without limit. If enough cells become cancerous, the organism dies. (Although i am primarily concerned with human cancer, it should be noted that other animals and even plants fall victim to cancer. Laboratory rodents protected from predators infection usually die of cancer.) As cancer cells multiply, they form lumps called tumors. (The scientific study of tumors is called oncology, derived from the Greek word onkos, business which means "a mass".) Tumors that are benign do not spread to other tissues, may cease to grow and are usually harmless. Skin warts are benign cancer tumors that are caused by viruses. Cancers are malignant when they spread to other tissues.
Although i use technical language in the technical sections on molecular biology and chemical carcinogenesis, i attempt to define or explain technical terms before i use them. Those who are most interested in the technical sections can still benefit from the background information in the non-technical section. The technical molecular biology sections can be skipped, but some reference to their content will be found in subsequent sections. Most of the information in this article is a summary of material that is available from textbooks, so i will not bother to provide detailed citations of my sources, except in cases concerning specific or controversial research. (return to contents) The human body is composed of approximately 200 different cell types that are required to accomplish specific functions. Cells in blood, skin, bone, muscle, best brain, etc. Must perform distinctive tasks to support the organism as a whole, which supplies them with nutrient, oxygen waste-removal service. Cancer is a disease of transformed cells.
is the cause of one-quarter of all deaths in developed countries. Everyone is at risk, but some more than others. The incidence of cancer increases exponentially with age to age. Two thirds of all people with cancer are over age. Before the age of 40 cancer strikes fewer than one person in fifty. Between ages 60 to 79 a third of men and a quarter of women develop cancer. Although cancer is rare in children between ages 1 and 14 (fatal disease is rare in children leukemia is the number one cause of death in that age group. ( leukemia is Latin for "white blood a reference to the milky appearance of the blood of persons whose white blood cells — leukocytes — have proliferated cancerously.) About half of those diagnosed with cancer are cured and about half are killed by the cancer. Cancer is a technical subject, but in the second section i attempt to give an overview of cancer without the technical language of cancer or cell biology.
Relative incidence of summary Cancer, by Organ System. Manifestations of Cancer, by Organ System. Lung Cancer, colon and Rectal Cancer, breast Cancer. Prostate cancer, cancer of the pancreas, stomach and Esphageal Cancer. Gynecologic (Ovarian, Uterine and Cervical) Cancer. Non-Hodgkin's Lymphoma, leukemia, liver Cancer, brain and Central Nervous System Cancer. Kidney cancer, urinary Bladder Cancer, multiple myeloma, skin Cancer (including Melanoma). Oral (Mouth, lip, tongue and Pharynx) Cancer. General Comments about Cancer Prevention, problems Proving that Substances cause cancer.
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Educational Resources by category and audience so you can easily find what you need, whether you are a government or utility looking for technical information, or students and educators looking for activities and lesson plans. Cancer death — causes prevention. Cancer death — causes prevention by ben Best, contents: links to sections by topic. Introduction, cancer overview in Non-Technical Language, molecular biology of Cancer causation. Oncogenes and Tumor-Suppressor Genes in Progression State. Cell Cycle control, signalling Molecules and Transcription Factors, inflammation and Cancer. Cancer Genetics and Tumor Viruses, epigenetic Dysregulation, carcinogenic Chemicals. Relative incidence of Cancer, by causative agent.