Seborrheic keratosis with basal clear cells: a distinctive microscopic mimic of melanoma in situ.
BACKGROUND
We observed seborrheic keratoses with many basilar clear cells, creating a microscopic pattern that mimicked a seborrheic keratosis involved by melanoma in situ.


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


METHODS
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.


RESULTS
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.


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


CONCLUSIONS
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.
Neuhaus
Isaac M
IM
Department of Dermatology, University of California, San Francisco, California, USA.
LeBoit
Philip E
PE
McCalmont
Timothy M
TM
D000368:Aged; D000369:Aged, 80 and over; D000906:Antibodies; D000951:Antigens, Neoplasm; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007106:Immune Sera; D007124:Immunoenzyme Techniques; D007633:Keratins / Q000276:immunology; D017492:Keratosis, Seborrheic / Q000378:metabolism / Q000473:pathology*; D058965:MART-1 Antigen; D008297:Male; D008545:Melanoma / Q000473:pathology*; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000276:immunology; D012189:Retrospective Studies; D009418:S100 Proteins / Q000276:immunology; D012878:Skin Neoplasms / Q000473:pathology*; D013194:Staining and Labeling
D000906:Antibodies; D000951:Antigens, Neoplasm; D007106:Immune Sera; D058965:MART-1 Antigen; C548667:MLANA protein, human; D009363:Neoplasm Proteins; D009418:S100 Proteins; D007633:Keratins