ATYPICAL KERATOSIS
There are surface tumors that have the architectural features of a seborrheic keratoses but there is cytologic atypia of the constituent cells. Some of these lesions  have areas within them that are composed of the cells usually found in seborrheic keratoses in addition to the atypical cells.  The atypia is bowenoid in some cases and of actinic keratosis type in others. Some of these cases appear to be examples wherein neoplastic changes are taking places in a seborrheic keratosis, but other cases may represent de novo architectural variants of the neoplastic or preneoplastic keratinocytes. I use the term 'atypical keratosis' unless there is actual bowenoid in situ carcinoma, and I recommend the destruction or removal of any residual clinical lesion.

 
Scan of lesion from the face showing the architectural features of a seborrheic keratosis.
Low power showing atypia of constituent keratinocytes in the central papillary structure. Note basaloid cells of seborrheic keratosis type on far right.
High power showing actinic keratosis type atypia.

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