Cancer
- There is also a constellation named Cancer: see Cancer (constellation).
Cancer is a disease where some of the body's own
cellss repeatedly divide without control as the result of a
mutation. The new cells may form a malignant
tumor (a
neoplasm) or propagate throughout the body.
Cancer has become an important problem with the rise in life expectancy, as the mutations become more likely the longer a person lives. Though great progress in treatment has been made, many cancers reach advanced stages remain incurable and ultimately fatal. Thankfully for patients with incurable cancer, the last 20 years have seen the widespread availability of
palliative care.
Cancer is treated by an
oncologist, a
doctor specialized in the treatment of malignant disease.
Prevention and early detection
\nBecause of the difficulty treating advanced cancer prevention and early detection of cancer remain important strategies to reduce cancer related illness and death.
Proven methods of decreasing the risk of cancer include smoking cessation and avoiding other known carcinogens such as sunlight, genital warts.
Accepted early detection strategies include:\n* breast self-examination and regular screening mammograms\n* Pap smears\n* testicular self-examination – for men from the age of 15 years\n* prostate examination +/- serum acid phosphatase levels\n* annual prostate specific antigen blood test\n* fecal occult blood test or stool guaiac testing and colonoscopy (above age 50, lower if risk factors present)
Genetic screening is likely to gain increasing prominence over the next decade
Both white and Green tea have been shown to help in preventing cancer in rats, but the significance of this in humans is unknown.
Forms of cancer
\nThere are many forms of cancer; they are grouped according to either their cell type or their location.
Cell types include:\n* adenoma - from glandular tissue\n* carcinomas - from epithelial cells\n** squamous cell carcinoma\n* leukemia - from bone marrow stem cells\n* lymphoma - from lymphatic tissue\n* melanoma - from melanocytes\n* sarcoma - from connective tissue, bone or muscle\n* teratoma - from germ cells
Majors cancers, by body location:\n* bladder carcinoma\n* blood (and bone marrow) - hematological malignancies\n** leukemia\n** lymphoma \n*** Hodgkin's disease\n*** non-Hodgkin's lymphoma\n** multiple myeloma\n* brain tumor\n* breast cancer\n* cervical cancer\n* colorectal cancer - in the colon, rectum, anus, or appendix\n* esophageal cancer\n* endometrial cancer - in the uterus\n* hepatocellular carcinoma - in the liver\n* gastrointestinal stromal tumor (GIST)\n* laryngeal cancer\n* lung cancer\n* mesothelioma - in the pleura or pericardium\n* oral cancer\n* osteosarcoma - in bones\n* ovarian cancer\n* pancreatic cancer\n* prostate cancer\n* renal cell carcinoma - in the kidneys\n* rhabdomyosarcoma - in muscles\n* skin cancer, including benign moles and dysplastic nevi\n* stomach cancer\n* testicular cancer\n* thyroid cancer
Treatment
\nTreatment of cancer typically involves surgery to remove tumors and nearby lymph nodes to which the cancer may have spread, combined with radiation therapy and/or chemotherapy. The latter two target cells in the body that are rapidly dividing. This includes the cancer cells but also certain healthy ones, which is the reason for the severe side effects of these treatments.
Biology of malignant tumors
Carcinogenesis
\nCarcinogenesis (lit.: creation of cancer) is the process of derangement of the rate of cell division.
Cancer is, ultimately, a disease of genes. Typically, a series of several mutations is required before a cell becomes a cancer cell. The process involves both oncogenes and tumor suppressor genes. Oncogenes promote cancer when "switched on" by a mutation, whereas tumor suppressor genes prevent cancer unless "switched off" by a mutation. Chromosomal translocation, such as the Philadelphia chromosome, is special type of mutation and may involve oncogenes or tumor suppressor genes.
Mutations can have various causes:\n* tobacco smoking\n* radiation, including ultraviolet radiation from the sun\n* chemicals called carcinogens\n* viral or bacterial infection, such as the Human papillomavirus viruses in cervical cancer and Helicobacter pylori bacteria\n* DNA damage by free radicals\n* inherited predisposition, such as the BRCA1 gene in breast cancer\n* chronic inflammation from any cause
Viruses play a role in about 15% of all cancers. Tumor viruses, such as some retroviruses and herpesviruses, usually carry some oncogene or tumor suppressor inactivating gene in their genome.
It is impossible to tell the initial cause for most of the cancers. However, with molecular biology, it is now possible to characterize the mutations within a tumor, and to a certain extent predict its behavior. For example, about half of the tumors are deficient in the tumor suppressor gene p53, also known as "the guardian of the genome". This mutation is associated with poor prognosis, since those tumor cells are less likely to go into apoptosis (programmed cell death) when damaged by therapy. There are more mutations that make a tumor more malignant. Telomerase mutations enable a tumor cell to divide indefinitely. Other mutations enable the tumor to grow new blood vessels to feed it, or to detach from the surrounding tissue, spreading to other parts of the body.
Malignant tumors cells, such as in carcinoma, sarcoma, lymphoma or leukemia, have distinct properties:\n* evading apoptosis\n* unlimited growth potential (immortalitization)\n* self-sufficiency of growth factors\n* insensitivity to anti-growth factors\n* increased cell division rate\n* altered ability to differentiate \n* no ability for contact inhibition\n* ability to invade neighbouring tissuess\n* ability to build metastases at distant sites\n* ability to promote blood vessel growth (angiogenesis)
A cell that degenerates into a tumor cell does usually not acquire all these properties at once, but its descendant cells are selected to build them. This process is called cellular evolution. A first step in the development of a tumor cell is usually a small change in the DNA, often a point mutation, which leads, among other things, to a genetic instability of the cell. The instability increases to a point where the cell loses whole chromosomes, or has double ones. Also, the DNA methylation pattern of the cell changes, activating and deactivating genes more or less at random. Cells that divide at a high rate, such as stem cells, show a higher risk of becoming tumor cells than those which divide less, for example neurons. If the initial tumor cell (or group of tumor cells) is not removed by the immune system, it becomes a cancer.
In cellular model systems, cells are exposed to carcinogenic influences (chemicals, radiation). In these systems, the first signs of a cell developing into a tumor cell are:\n# Immortality. The usual number of cell divisions for a mammalian cell is 50-60 (cell senescence), then it ceases to divide. Tumor cells keep dividing forever.\n# Altered morphology.\n# Building of cellular clusters (foci).\n# Loss of contact inhibition.\n# Low or no need for growth factors.
Items 2-4 (above) can sometimes be traced to mutations in genes that result in a disruption of cell adhesion. Some cell adhesion proteins are tumor suppressor genes.
Metastasis
\nCancers are capable of spreading through the body by either local invasion or distant metastasis. Invasion is the direct migration and penetration by cancer cells into neighboring tissues. Metastasis is the process of cancer cells penetrating into lymphatic and blood vessels, circulating through the bloodstream, and then invading normal tissues elsewhere in the body. Cancer is most dangerous when it metastasizes. When malignant tissue is surgically removed, some local lymph nodes are typically removed and dissected to give an idea of if and how much the cancer is spreading.
Cancer research agencies and funding bodies
\nBelow is a list of some well-known institutions dedicated to funding cancer research:\n* American Cancer Society\n* BC Cancer Agency\n* Cancer Research UK\n* Canadian Cancer Society\n* International Agency for Research on Cancer\n* National Cancer Institute (US)\n* Yorkshire Cancer Research
See also
\nList of cancer patients -- Oncology -- Terminal illness -- Palliative care
External links
\n* Cancer News from Genome News Network (GNN)\n* National Cancer Institute\n*Cancer from the Open Directory Project\n*Cancer Medicine, online textbook.
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Category:Oncology
