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Keratoacanthoma

Keratoacanthoma is a relatively common low-grade malignancy that originates in the pilosebaceous glands. It clinically and pathologically resembles squamous cell carcinoma.1 Keratoacanthoma rarely progresses into an invasive squamous cell carcinoma. Keratoacanthoma may serve as a marker for the important autosomal dominant familial cancer syndrome, the Muir-Torre syndrome.1

Epidemiology
  • Incidence is estimated at 1 in 1000.
  • Peak incidence occurs in those aged over 60 years. Is rare in young adults.
  • Uncommon in darker-skinned patients.
  • Males are twice as often affected as females.
  • Epidemiological data is similar to squamous cell carcinoma and Bowen disease in terms of age, sex and the site of lesions.

Risk factors

  • Sunlight and chemical carcinogens have been implicated.
  • Trauma, genetic factors and immunocompromised status have also been associated.2
  • Industrial workers exposed to pitch and tar have a higher incidence of both keratoacanthoma and squamous cell carcinoma.
Presentation
  • Typically rapid growth over a few weeks to months, followed by a slow spontaneous resolution over 4-6 months (but may take up to 1 year).
  • Most occur on sun-exposed areas, e.g. face, neck, and dorsum of hands and forearms.
  • Usually solitary and begin as firm, round, skin-coloured or reddish papules that rapidly progress to dome-shaped nodules with a smooth shiny surface. A central crater of ulceration may develop, or a keratin plug that may project like a horn.
  • Leaves a residual scar if not excised.
  • Occasionally presents as multiple tumours and may enlarge to up to 15 cm, become locally aggressive and metastasise.



KERATOCANTHOMA - NOTE CENTRAL KERATIN PLUG (OM2336a.jpg)


Differential diagnosis
  • Squamous cell carcinoma
Investigations
  • Shave biopsy of keratoacanthoma is indistinguishable from invasive squamous cell carcinoma. Therefore, excisional or deep incisional biopsy is required.
Associated diseases
  • The Muir-Torre syndrome includes the presence of sebaceous gland tumours, with or without keratoacanthomas, and associated with visceral malignancies, especially colorectal. It has autosomal dominant inheritance.3,4
Management
  • Complete excision is the treatment of choice for all skin neoplasms thought to be keratoacanthoma.5
  • 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.

Radiotherapy

  • Keratoacanthomas are radiosensitive and respond well to low doses of radiation.
  • Radiation therapy may be useful in selected patients with large tumours when resection will result in cosmetic deformity, or for tumours that have recurred following attempted excision.
  • Both laser therapy and cryotherapy have been used successfully in small keratoacanthomas.
Complications
  • Reportedly progresses, although rarely, to invasive or metastatic carcinoma.
Prognosis
  • Prognosis is excellent following excisional surgery.
  • Without surgery, prognosis is usually good but has recently been reclassified as squamous cell carcinoma-keratoacanthoma type to reflect the difficulty in histologic differentiation, as well as the uncommon but potentially aggressive nature of keratoacanthoma.
  • Increased risk for developing subsequent non-melanoma skin cancer.6
Prevention
  • Patient education in sun-protection techniques

Document references
  1. Schwartz RA; Keratoacanthoma: a clinico-pathologic enigma. Dermatol Surg. 2004 Feb;30(2 Pt 2):326-33; discussion 333. [abstract]
  2. Clausen OP, Beigi M, Bolund L, et al; Keratoacanthomas frequently show chromosomal aberrations as assessed by comparative genomic hybridization. J Invest Dermatol. 2002 Dec;119(6):1367-72. [abstract]
  3. Ponti G, Losi L, Di Gregorio C, et al; Identification of Muir-Torre syndrome among patients with sebaceous tumors and keratoacanthomas: role of clinical features, microsatellite instability, and immunohistochemistry. Cancer. 2005 Mar 1;103(5):1018-25. [abstract]
  4. Muir-Torre Syndrome, OMIM
  5. Manstein CH, Frauenhoffer CJ, Besden JE; Keratoacanthoma: is it a real entity? Ann Plast Surg. 1998 May;40(5):469-72. [abstract]
  6. Graells J; The risk and risk factors of a second non-melanoma skin cancer: a study in a Mediterranean population. J Eur Acad Dermatol Venereol. 2004 Mar;18(2):142-7. [abstract]
Internet and further reading Acknowledgements EMIS is grateful to Dr Colin Tidy for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2007.
DocID: 2977
Document Version: 20
DocRef: bgp2336
Last Updated: 21 Nov 2007
Review Date: 20 Nov 2009








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PS - Health and Poverty

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