Diagnostic utility of SOX10 immunostaining in benign lichenoid keratosis: A study of 21 cases

Abstract

Background Benign lichenoid keratosis (BLK) is a cutaneous lesion that can clinically mimic malignancy and may represent regression of a pre‐existing lesion. BLK may show epidermal pseudo‐nests prompting evaluation for a melanocytic lesion. False positivity of MART‐1/Melan‐A immunostaining in pseudonests has been showed; however, the value of SRY‐related HMG‐box 10 (SOX10) staining in BLK with features suspicious for a melanocytic proliferation has not been previously reported. Methods Twenty‐one cases of BLK from 2015 to 2020 were identified. Slides were reviewed and SOX10 immunohistochemistry was performed on each case. Subsequently, Melan‐A immunohistochemical staining was performed on all cases. Results In 10 cases (47.6%), unexpected SOX10 staining was seen in rare to numerous small, single cells in the epidermis above the basal cell layer. No malignancy was identified. Of the 10 cases, 8 (80%) showed suprabasal SOX10 staining did not show similar suprabasal Melan‐A staining; 2 (20%) cases showed scattered suprabasal cells positive for Melan‐A. Conclusion SOX10 immunostaining in BLK can highlight scattered cells in the epidermis (not easily noticeable on routine stain). Performing SOX10 immunostain alone on BLK can prompt a misdiagnosis of a melanocytic lesion and should be done with caution.