Which histologic findings are characteristic of clonal seborrheic keratosis?

Updated: Oct 14, 2020
  • Author: Arthur K Balin, MD, PhD, FACP; Chief Editor: William D James, MD  more...
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The clonal seborrheic keratoses show well-demarcated nests of basaloid or larger squamous cells within an acanthotic seborrheic keratoses. Melanoacanthoma is a deeply pigmented seborrheic keratosis in which an acanthotic proliferation of large dendritic melanocytes is identified. It probably represents a concomitant proliferation or activation of the dendritic melanocytes and epidermal cells. Lichenoid seborrheic keratosis is an inflammatory variant. In one study of 108 seborrheic keratoses, 66% were acanthotic, 25% were hyperkeratotic, and 9% had a reticulated (adenoid) pattern. In this study, 5.5% (6/108) of the specimens contained squamous cell carcinoma and 4 of these appeared to develop within the central portion of the lesion. Also, 4 of the 6 malignancies developed in the reticulated type of seborrheic keratoses.

In irritated seborrheic keratoses, pronounced squamous metaplasia can occur, which may be misdiagnosed as basosquamous carcinoma. This phenomenon is not due to human papillomavirus. [28] Human papillomavirus can be identified in the seborrheic keratoses of patients with epidermodysplasia verruciformis and in seborrheic keratosis–like lesions exhibiting bowenoid changes. These probably should be considered as condylomata rather than as true seborrheic keratoses. [29, 30]

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