Keratoacanthoma

Keratoacanthoma: Description, Causes and Risk Factors:A rapidly growing tumor that may be umbilicated, and usually occurs on exposed areas of the skin in elderly white men, which invades the dermis but remains localized and usually resolves spontaneously if untreated; microscopically, the nodule is composed of well-differentiated squamous epithelium with a central keratin mass that opens on the skin surface.KeratoacanthomaThe pathogenesis of keratoacanthoma is not completely understood, but the tumor is thought to originate from the pilosebaceous unit; most consider it a form of squamous cell carcinoma. There are some reports of keratoacanthoma arising over sites of trauma, burn scars, and sites submitted to cryotherapy for actinic keratosis. Recently, the association of keratoacanthomas with tattoos has been reported.The distribution of lesions in suns exposed areas dictates a major role for solar radiation. It has been postulated that in genetically predisposed individuals, the sunlight may activate an oncogene or it may inactivate a suppressor gene. Regression of KA is likely to be mediated by activated CD4+ T lymphocytes, possibly via cytokine secretion.Risk Factors:Sunlight and chemical carcinogens have been implicated.
  • Trauma, genetic factors and immunocompromized status have also been associated.
  • Industrial workers exposed to pitch and tar have a higher incidence of both keratoacanthoma and SCC.
The exact incidence of the disease is unknown, but it is more common in White & European-American descents.Symptoms:Clinically, it appears as a small erythematous nodule which grows rapidly over 3 to 4 weeks to reach a size of 2-3 cm in diameter. Central ulceration occurs commonly giving a central crater surrounded by a heaped shoulder. The lesion usually involutes over 2 to 3 months leaving an unsightly irregular scar.Histologically, the following features are seen:Cup-shaped lesion with a central mass of keratin.
  • Acanthotic (hyperplastic) epidermis which has a sharp demarcation from the adjacent normal Skin. The cells appear large and pale with small nuclei.
  • Base of the lesion is well demarcated from the adjacent dermis by inflammatory response.
Diagnosis:Histologically, the epidermis may be ulcerated with marked cellular atypia and loss of polarity. At the base of the lesion, invasive tongues of epithelial cells are seen, as well as clumps of epithelial cells, detached from the main tumor mass. Compared with keratoacanthoma, there is no marked shouldering and the leukocyte abscesses are absent.Treatment:Complete excision is the treatment of choice for all skin neoplasms thought to be keratoacanthoma. Medical treatment is reserved for when surgical intervention is not possible, e.g. multiple lesions not amenable to surgery because of size or location. Treatments that have produced some success include systemic retinoids (e.g. isotretinoin), intralesional methotrexate, 5-fluorouracil, bleomycin and steroids, and topical imiquimod and 5-fluorouracil (5-FU).Keratoacanthomas are radiosensitive and respond well to low doses of radiation. Radiation therapy may be useful in selected patients with large tumors when resection will result in cosmetic deformity, or for tumors that have recurred following attempted excision. Both laser therapy and cryotherapy have been used successfully in small keratoacanthoma.Prognosis is excellent following excisional surgery.NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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