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6 November 2013 - Case #290

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Thanks to Dr. Vasiliki Tzelepi, University of Patras (Greece), for contributing this case.

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Case #290

Clinical history:
An 87 year old woman presented with a forearm skin lesion, present for about one year without any changes, measuring 2.7 x 1.8 x 0.7 cm. It was excised.

Microscopic images:

What is your diagnosis?

Click here for diagnosis and discussion:

Diagnosis: Squamous cell carcinoma, keratoacanthoma-like

Keratoacanthoma (KA) is a hair follicle derived neoplasm occurring in the sun-exposed skin of the elderly, considered by many a well differentiated form of invasive squamous cell carcinoma, but by others a benign squamous proliferation (Semin Diagn Pathol 2009;26:150). It typically arises from normal skin, grows rapidly for 4 - 8 weeks, then regresses over 6 months to leave a depressed, annular scar (eMedicine: Keratoacanthoma [Accessed 28 March 2024]). It only rarely metastasizes.

Grossly, keratoacanthoma is a flesh colored, dome shaped lesion with a distinctive central, keratin filled crater. Its histology varies over time. Early, it is composed of well circumscribed solid lobules of large, pale squamous cells with little keratinization and only mild atypia. In the stable phase, it has a central crater filled with keratin but no granular layer. The squamous nests are larger, more irregular and infiltrative and are accompanied by a marked inflammatory infiltrate with lichenoid features. There may be marked atypia, mitotic figures, atypical mitotic figures at the periphery, perineural invasion and rarely vascular invasion (Australas J Dermatol 2001;42:168, Dermatol Pract Concept 2012;2:204). In the regressing phase, the keratin filled crater becomes flatter and decreases in diameter. Keratinocytes appear banal and lack glassy pink cytoplasm and inflammation subsides (J Am Acad Dermatol 2012;67:1008).

Classification of keratoacanthoma-like lesions is controversial and includes classic keratoacanthoma, keratoacantoma-like squamous cell carcinoma, keratoacanthoma with malignant transformation and other crateriform cutaneous lesions (J Dermatol 2013;40:443). In this case report, the lesion has features of invasive carcinoma including deep infiltration almost to the subcutis and marked atypia. It lacks classic features of keratoacanthoma, including a keratin-filled crater, overhanging edges and a hemispheric shape. Treatment is primarily surgical, with medical treatment (intralesional methotrexate, steroids, imiquimod, 5-FU) reserved for nonsurgical cases (Can J Plast Surg 2011;19:e15).

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