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Keratoacanthoma (KA) is a common low-grade (unlikely to metastasize or invade) skin tumour that is believed to originate from the neck of the hair follicle.〔Fisher, B.K., Elliot, G.B. Keratoacanthoma: Reflections on an Unusual Lesion. Can Med Assoc J. 1965 August 7; 93(6): 272–273.〕 The defining characteristic of KA is that it is dome-shaped, symmetrical, surrounded by a smooth wall of inflamed skin, and capped with keratin scales and debris. It grows rapidly, reaching a large size within days or weeks, and if untreated for months will almost always starve itself of nourishment, necrose (die), slough, and heal with scarring. KA is commonly found on sun-exposed skin, often face, forearms and hands.〔Schwartz RA. The Keratoacanthoma: A Review. J Surg Oncol 1979; 12:305–17.〕 Under the microscope, keratoacanthoma very closely resembles squamous cell carcinoma. In order to differentiate between the two, almost the entire structure needs to be removed and examined. While some pathologists classify KA as a distinct entity and not a malignancy, about 6% of clinical and histological keratoacanthomas do progress to invasive and aggressive squamous cell cancers; some pathologists may label KA as "well-differentiated squamous cell carcinoma, keratoacanthoma variant", and prompt definitive surgery may be recommended.〔Ko CJ, Keratoacanthoma: facts and controversies. Clin Dermatol. 2010; 28(3):254–61 (ISSN: 1879-1131)〕〔http://www.emedicine.com/derm/topic206.htm〕〔Kossard S; Tan KB; Choy C; Keratoacanthoma and infundibulocystic squamous cell carcinoma. Am J Dermatopathol. 2008; 30(2):127–34 (ISSN: 1533-0311)〕〔Weedon DD, et al. Squamous cell carcinoma arising in keratoacanthoma: a neglected phenomenon in the elderly. Am J Dermatopathol. 2010; 32(5):423–6〕 == Classification == Keratoacanthomas (molluscum sebaceum) may be divided into the following types:〔Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. ISBN 0-07-138076-0.〕〔James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatology''. (10th ed.). Saunders. ISBN 0-7216-2921-0.〕 * ''Giant keratoacanthomas'' are a variant of keratoacanthoma, which may reach dimensions of several centimeters.〔 * ''Keratoacanthoma centrifugum marginatum'' is a cutaneous condition, a variant of keratoacanthomas, which is characterized by multiple tumors growing in a localized area.〔〔 * ''Multiple keratoacanthomas'' (also known as "Ferguson–Smith syndrome," "Ferguson-Smith type of multiple self-healing keratoacanthomas,") is a cutaneous condition, a variant of keratoacanthomas, which is characterized by the appearance of multiple, sometimes hundreds of keratoacanthomas.〔〔 * A ''solitary keratoacanthoma'' (also known as "Subungual keratoacanthoma") is a benign, but rapidly growing, locally aggressive tumor which sometimes occur in the nail apparatus.〔〔 * ''Generalized eruptive keratoacanthoma'' (also known as "Generalized eruptive keratoacanthoma of Grzybowski") is a cutaneous condition, a variant of keratoacanthomas, characterized by hundreds to thousands of tiny follicular keratotic papules over the entire body.〔〔 Treatments are not successful for many patients with Generalized eruptive keratoacanthoma. Use of emollients and anti-itch medications can ease some symptoms. Improvement or complete resolutions of the condition has occurred with the application of the following medications: Acitretin, Isotretinoin, Fluorouracil, Methotrexate, Cyclophosphamide. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Keratoacanthoma」の詳細全文を読む スポンサード リンク
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