Abstract

Benign lichenoid keratosis (BLK) is a cutaneous lesion that can clinically mimic cutaneous malignancy. Histologically, it is characterized by lichenoid interface dermatitis and may represent regression of a pre-existing lesion. BLK may show dermal or epidermal pseudo-nests which prompt rule out of a regressing melanocytic lesion. Previous reports have demonstrated the phenomenon of false positive Melan-A and MART-1 staining in such pseudo-nests and have chronicled the subsequent diagnoses of these lesions as BLK. SRY-related HMG-box 10 (SOX10) is a nuclear transcription factor expressed in cells of neural crest origin. It is a highly sensitive marker for melanocytes; however, it is not 100% specific. While Melan-A and MART-1 have begun to be catalogued, the utility of performing SOX10 on BLK when suspicious for a melanocytic proliferation has not yet been described. 22 cases of BLK from 2015-2020 were retrospectively identified. Hematoxylin and eosin (H&E) stained slides were reviewed and SOX10 immunohistochemistry was performed on each case with appropriate controls. In 10 cases, (45.5%) unexpected positive staining was seen in numerous small, single cells of the epidermis above the basal cell layer. On routine H&E staining, the highlighted cells were not readily appreciated and no obvious pagetoid spread or confluent melanocytic growth were identified. Based on our study, SOX10 immunostaining performed on BLK can highlight scattered cells in the epidermis that would otherwise not be flagged as atypical on routine staining. These SOX-10 positive cells may represent benign “passenger” melanocytes. We aimed to assess one institution’s experience with SOX10 immunohistochemical staining specificity on lichenoid keratoses. Moreover, we highlight the importance of careful histologic correlation in these lesions and underscore a possible diagnostic pitfall — SOX10 single intraepidermal cells in BLK could be misinterpreted as a melanocytic lesion with pagetoid spread.

Financial Disclosure:
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