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J Am Acad Dermatol. 2006 Jan;54(1):132-5.

Seborrheic keratosis with basal clear cells: a distinctive microscopic mimic of melanoma in situ.

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  • 1Department of Dermatology, University of California, San Francisco, California, USA.



We observed seborrheic keratoses with many basilar clear cells, creating a microscopic pattern that mimicked a seborrheic keratosis involved by melanoma in situ.


We sought to report a series of these seborrheic keratoses and the immunohistochemical stains used to reach a proper diagnosis.


We reviewed 9 cases of seborrheic keratosis that had a distinctive pattern of basal clear cells with ample cytoplasm. All cases were evaluated by conventional microscopy, and Melan-A, S-100, and high molecular weight keratin 903 immunostains.


The basal clear cells failed to react with Melan-A and S-100 protein antisera. In contrast, these cells labeled with an antikeratin antibody in all cases. In all, 7/9 (78%) showed immunopositivity only at the peripheries of cells, creating a pattern that could be mistaken for a negative stain if not examined at high magnification.


This is a retrospective review of cases limited to a large referral dermatopathology service.


We describe a previously uncharacterized pattern of seborrheic keratosis that can microscopically mimic melanoma in situ. Careful conventional microscopy coupled with a panel of immunostains can allow the proper diagnosis to be reached.

[PubMed - indexed for MEDLINE]
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