Cancer: Difference between revisions

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'''Cancer''' refers to a wide variety of diseases that have in common ''uncontrolled cell proliferation''. 
Malignant growth entails uncontrolled cell division, lack of normal cell death (apoptosis), and failure of the cells' environment to help control its growth.  At a certain point, a cancer can also gain the ability to escape from its point of origin and "metastisize", or spread. As clumps of cancer cells grow, then can form "tumors".  Not all cancers form tumors.  For instance, in most leukemias, the cancer cells are circulating through the blood, rather than forming discrete masses.  Cancers, especially rapidly growing ones, can consume a great deal of energy, and can secrete various substances that cause a general decline in health.
Cancer can cause symptoms in a number of ways: by direct effect on the organ involved (i.e. a cough with lung cancer), by growing into a vital structure (i.e. prostate cancer obstructing the urethra), or by causing generalized malaise and anorexia. This last topic is less well understood.
Since cancers arise from so many different cell types, treatments are often very specific.  There is no one treatment for "cancer". 
==Classification==
Cancers are generally classified by the cell and/or tissue type of origin, and Latin or Greek prefixes are often used to name the tissue involved. English names are used frequently for common cancers. For example, an [[epithelial]]-derived cancer in the [[bowel]] is a "colon [[carcinoma]]".  A [[mesothelial]]-derived cancer in the bone is an "[[osteosarcoma]]" (the prefix "osteo-" refers to bone). Other terms that refer to cancer are "malignancy" and "malignant neoplasm" (or simply neoplasm, although neoplasm can also refer to benign growths).
The following general categories are usually accepted:
* [[Carcinoma]]: malignant tumors derived from [[epithelium|epithelial]] cells. This group represents the most common cancers, including the common forms of [[breast]], [[prostate]], [[lung]] and [[colon]] cancer.
* Hematologic malignancies, including [[lymphoma]] and [[leukemia]]: malignant tumors derived from [[blood]] and [[bone marrow]] cells
* [[Sarcoma]]: malignant tumors derived from [[connective tissue]], or [[mesenchyme|mesenchymal]] cells
* [[Mesothelioma]]: tumors derived from the [[mesothelium|mesothelial]] cells lining the [[peritoneum]] and the [[pleura]].
* [[Glioma]]: tumors derived from [[glia]], the most common type of [[brain]] cell
* [[Germinoma]]: tumors derived from germ cells, normally found in the [[testicle]] and [[ovary]]
* [[Choriocarcinoma]]: malignant tumors derived from the [[placenta]]
Tumors are named using '''-oma''' as a suffix with the organ name as the root. For instance, a benign tumor of the smooth muscle of the uterus is called "leiomy'''oma'''" (the common name of this frequent tumor is ''fibroid''). If the tumor is malignant, the appropriate suffix is added, for example, "leiomyo'''sarcoma'''" is the cancerous version of a fibroid tumor.
This introductory article will give a brief description of what a [[Malignancy|malignancy]] is, and how cells are thought to ''become'' malignant. That understanding is important as a basis to comprehend the medical and surgical treatment of cancers, and effective approaches to their prevention. After a general introduction to malignancies, major types of carcinomas (epithelial malignancies) are surveyed, with links provided for further information. The clinical emphasis is on human cancers, but references to cancers in other species of animals is also made. Although the frequencies and the aggresiveness of the various types of cancers vary according to species, generally, the basic biology of cancers is true for all species of vertebrate animals, including humans and domestic animals.
==Cancer vs. other tumors==
Many types of growths can be found on and in the human body.  The term ''neoplasm'' is generally used for any abnormal growth.  Not all growths, however, are cancerous, or ''malignant''. Historically, illnesses of human and animals that were progressive and fatal, and that involved tumors that destroyed flesh, were well known. Although the word "cancer" has been used to describe such conditions, today the term cancer is only used when ''malignant'' cells are present in the body. Many processes can cause the body to form masses (lumps), including [[Infectious Diseases|infections]], and scarring from trauma and burns. Since malignant cells can almost always be recognized under the microscope, if the tissue is properly prepared, a [[Biopsy|biopsy]] is virtually always required to make a firm diagnosis of cancer.
===Types of Biopsies: Incisional & Excisional===
There are two general types of biopsies: incisional and excisional. If an area is suspicious for a possible malignancy, and it is both small and accessible, the entire lesion is usually removed in the biopsy. So, for example, a small freckle of the skin that shows signs of possible [[Melanoma|melanoma]] would be removed completely, rather than simply sampled. On the other hand, if excision would entail extra risk to the patient or is better done in continuity with other structures of the body, such as lymph nodes or bone, then an incisional biopsy, in which only a relatively small portion of the lesion is removed, is a better choice.
==Malignancy: How do malignant cells develop?==
===carcinogens are mutagens===
"Cancer can be defined as a genetic disease at the cellular level" <ref name=Harrisons>J. Larry Jameson, Peter Kopp:Chapter 56. Principles of Human Genetics. Harrison's Online Featuring the complete contents of Harrison's Principles of Internal Medicine, 16th Edition (Dennis L. Kasper, Eugene Braunwald, Anthony S. Fauci, Stephen L. Hauser, Dan L. Longo, J. Larry Jameson, and Kurt J. Isselbacher, Eds.)Copyright © 2005. Mcgraw-Hill's Access Medicine)</ref> That's because the rate of cell division and the amount of differentiation of a cell are controlled by genes. When mature cells become more like embryonic cells, they are said to de-differentiate. Although this process is not thought to be the exact opposite of differentiation of cells, it does describe the loss of characteristics of mature cells that cancer cells undergo.
===DNA repair===
When DNA is damaged in normal cells, by such environmental processes as exposure to sunlight or by errors that occur in cell division, then, ideally, repairs are made and normal DNA is restored. If there are defects in the ability of a cell to repair DNA, this can lead to the daughters of that cell eventually becoming malignant. Since a small number of defects are expected to occur with each cell division, an inability to repair them can lead to more and more abnormalities in successive generations of cells.
====Oncogenes====
==Common malignancies that are not epithelial cancers==
==Important forms of epithelial cancers==
===Skin Cancer===
====Basal cell carcinoma====
====Squamous cell carcinoma (skin)====
===Head & Neck Cancer===
====Mouth, throat and larynx====
====Esophagus====
====Thyroid gland====
===Lung Cancer===
===Breast Cancer===
===Colon Cancer===
===other gastrointestinal cancers===
===Prostate cancer===
===Brain tumors (cancers)===
==Oncology,Hematology and specialties that treat cancer ==
The two medical specialties that focus on malignancies are oncology and hematology. [[Oncology|Oncologists]] are physicians who are fully trained in [[Internal Medicine]] and have further training in the treatment of malignant tumors, primarily solid tumors. [[Hematology|Hematologists]] are also physicians who are fully trained in Internal Medicine, in their case further training is in disorders of the [[Blood|blood]], including the [[Bone marrow|bone marrow]], which produces blood cells. Both hematologists and oncologists have advanced training in giving the drugs that inhibit cancer growth, called [[Chemotherapy|chemotherapy]].
Some types of cancers and other malignancies are at least equally the province of other specialists, because of the part of the body they affect, or because the treatments they require, are the focus of those particular specialties. So, for example, [[Radiation Oncology|radiation oncologists]], who are trained in the use of external beam radiation and other kinds of radiation treatments, and surgeons who are specialists in the areas of the body that the cancer affects, like the breast or larynx, are important in cancer care, and depending on the type and extent of the cancer, may be the main physician directing the cancer patient's care. For several decades, the notion of a "team approach" has been embraced in the treatment of cancer. A team approach offers the support of an entire group of professionals, including the physicians of the specialties mentioned, nurses, social workers and others. The team also includes diagnostic physicians, like surgical pathologists and diagnostic radiologists who have special expertise in evaluation of the studies important for confirming and staging cancer.
==Prevention==
==Prevention==
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A [[randomized controlled trial]] of calcium that was not addressed in the Cochrane review above suggests benefit; however, the contribution of co-administered vitamin D cannot be separated.<ref name="pmid17556697">{{cite journal |author=Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP |title=Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial |journal=Am. J. Clin. Nutr. |volume=85 |issue=6 |pages=1586–91 |year=2007 |month=June |pmid=17556697 |doi= |url=http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=17556697 |issn=}}</ref>
A [[randomized controlled trial]] of calcium that was not addressed in the Cochrane review above suggests benefit; however, the contribution of co-administered vitamin D cannot be separated.<ref name="pmid17556697">{{cite journal |author=Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP |title=Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial |journal=Am. J. Clin. Nutr. |volume=85 |issue=6 |pages=1586–91 |year=2007 |month=June |pmid=17556697 |doi= |url=http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=17556697 |issn=}}</ref>
== References==
<references/>
==External links==
Topics in Cancer - provided by the National Institutes of Health (USA) [http://www.cancer.gov/cancertopics]
National Health Service site for general patient information (UK). Search for cancer in "questions" and "encyclopedia" [http://www.nhsdirect.nhs.uk/]
==Further reading==

Revision as of 23:10, 28 January 2009

Prevention

Systematic reviews by the Cochrane Collaboration regarding supplements for the the prevention of cancer
Intervention Type of cancer Conclusion
Calcium+vitamin D[1] Colorectal cancer "Although the evidence from two RCTs suggests that calcium supplementation might contribute to a moderate degree to the prevention of colorectal adenomatous polyps, this does not constitute sufficient evidence to recommend the general use of calcium supplements to prevent colorectal cancer"
Antioxidants[2] Gastrointestinal cancer • "We could not find convincing evidence that antioxidant supplements prevent gastrointestinal cancers"
• "Antioxidant supplements seem to increase overall mortality"
• "The potential cancer preventive effect of selenium should be tested in adequately conducted randomised trials."

Subsequent randomized controlled trials of antioxidants have also been negative, including not finding benefit from selenium.[3][4]

A randomized controlled trial of calcium that was not addressed in the Cochrane review above suggests benefit; however, the contribution of co-administered vitamin D cannot be separated.[5]

  1. ↑ Weingarten MA, Zalmanovici A, Yaphe J (2008). "Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps". Cochrane Database Syst Rev (1): CD003548. DOI:10.1002/14651858.CD003548.pub4. PMID 18254022. Research Blogging.
  2. ↑ Bjelakovic G, Nikolova D, Simonetti RG, Gluud C (2008). "Antioxidant supplements for preventing gastrointestinal cancers". Cochrane Database Syst Rev (3): CD004183. DOI:10.1002/14651858.CD004183.pub3. PMID 18677777. Research Blogging.
  3. ↑ Gaziano JM, Glynn RJ, Christen WG, et al (January 2009). "Vitamins E and C in the prevention of prostate and total cancer in men: the Physicians' Health Study II randomized controlled trial". JAMA 301 (1): 52–62. DOI:10.1001/jama.2008.862. PMID 19066368. Research Blogging.
  4. ↑ Lippman SM, Klein EA, Goodman PJ, et al (January 2009). "Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT)". JAMA 301 (1): 39–51. DOI:10.1001/jama.2008.864. PMID 19066370. Research Blogging.
  5. ↑ Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP (June 2007). "Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial". Am. J. Clin. Nutr. 85 (6): 1586–91. PMID 17556697. [e]
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