3.2.2 Keratoacanthoma

Grading & Level of Importance: B




Pseudocarcinoma; Verrucous carcinoma.


Quite common tumor mostly affecting males (>F) with fair skin over 60 years. Smoking and solar damage are a risk factors.


Keratoacanthoma (KA) is a clinically benign (no metastases) proliferation of highly differentiated squamous cells arising on normal skin. It belongs to the group of so-called pseudocarcinomas: papillomatosis carcinoides (carcinoma verrucosum), florid oral papillomatosis, genital condylomata gigantea (Buschke-Löwenstein), epithelioma (carcinoma) cuniculatum (L. Ackerman) of the foot, and papillomatosis cutis carcinoides (Gottron).

Aetiology & Pathogenesis

Human papilloma virus (HPV types 16, 21, others) infection in 25% of cases. UV-light may play a pathogenetic role. Transforming growth factor beta receptor 1  ( TGFBR1) can cause multiple self healing squamous cell carcinoma. In multiple, familial, and syndromatic cases an autosomal-dominant inheritance is discussed. Proliferation of epithelial cells with strong keratinization.

Signs & Symptoms

Rapidly growing (weeks) dome shaped solitary nodule, with a central crater filled with keratotic and necrotic material. Even though sun exposed skin is preferentially involved, the underlying skin is normal (no scarring). Rare variants include flat and migratory lesions with elevated margins, aggregated or generalized forms. Association with other symptoms is seen in Muir-Torre-syndrome.


Developing on normal skin, in contrast to malignant squamous cell carcinoma, which always develops on predamaged skin (scars). Head and neck most common sites, followed by extremities. Rarely the oral cavity is affected.


This includes other pseudocarcinomas

  • Solitary keratoacanthoma (most frequent type)
  • KA centrifugum marginatum
  • Multiple generalized or aggregated keratoacanthomas (Ferguson-Smith; Grzybowski)
  • Syndromic keratoacanthomas (Muir-Torre-syndrome)
  • Papillomatosis cutis carcinoides (Gottron)
  • Giant keratoacanthomas (Buschke-Löwenstein)
  • Intraoral and mucosal keratoacanthoma

Laboratory & other workups

None specific. Biopsy.


Revealing of the typical features only in full size biopsies or excisions: symmetrical cup‐shaped tumor, filled with cornified debris and with smooth outer margins; central keratotic plug with massive acanthosis and papillomatosis; bilateral epithelial lip formation of adjacent rete ridges; proliferation of atypical keratinocytes and mitoses; intraepidermal formation of microabscesses, filled with mixed inflammatory cells and debris; mixed cellular infiltrate in the dermis. Necrotic masses in regressing lesions.


Developing within a few weeks, in contrast to malignant squamous cell carcinoma, which develops over months. Clinically benign with tendency for spontaneous regression; no metastasis.


Scarring. Misdiagnosis of fast growing malignant squamous cell carcinoma.


Diagnosis relies on clinical features and histology.

Differential diagnosis

Squamous cell carcinoma, nodular basal cell carcinoma, verruca vulgaris, prurigo nodularis and hypertrophic lichen planus in disseminated types of KA,  tumors of skin appendages.

Prevention & Therapy

Wait and see. Biopsy often leads to spontaneous regression. Intralesional injection of glucocorticosteroids (leads to apoptosis of cells) or methotrexate. If still growing removal by surgical excision.


Radiotherapy is ineffective because of the high cellular differentiation and even may induce malignant transformation.

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