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

Epidemiology²

• Incidence is estimated at 1 in 1,000.
• Peak incidence occurs in those aged over 60 years. Is rare in young adults.
• It is uncommon in darker-skinned patients.
• Males are twice as often affected as females.
• Epidemiological data are similar to squamous cell carcinoma (SCC) and Bowen's 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.³
• Industrial workers exposed to pitch and tar have a higher incidence of both keratoacanthoma and SCC.

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. the face, neck, and dorsum of hands and forearms.
• They are 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.
• It 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.

Differential diagnosis

• Squamous cell carcinoma (SCC)
• Basal cell carcinoma
• Actinic keratosis
• Seborrhoeic keratosis

Investigations

• Shave biopsy of keratoacanthoma is indistinguishable from invasive squamous cell carcinoma (SCC). 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.^4,5

Management

• Complete excision is the treatment of choice for all skin neoplasms thought to be keratoacanthoma.⁶
• 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 it has recently been reclassified as squamous cell carcinoma (SCC)-keratoacanthoma type to reflect the difficulty in histological differentiation, as well as the uncommon but potentially aggressive nature of keratoacanthoma.
• There is increased risk for developing subsequent nonmelanoma skin cancer.⁷

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. Chuang Tsu-Yi; Keratoacanthoma; eMedicine, March 2009.
3. 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]
4. 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]
5. Muir-Torre Syndrome, OMIM
6. Manstein CH, Frauenhoffer CJ, Besden JE; Keratoacanthoma: is it a real entity? Ann Plast Surg. 1998 May;40(5):469-72. [abstract]
7. 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

• Keratoacanthoma, DermNet NZ
• Torre-Muir syndrome, DermNET NZ

Acknowledgements