The detectability of intraepidermal melanocytes-A narrative review of immunohistochemical studies

Some intraepidermal lesions, even the nonmelanocytic ones, may mimic melanoma in situ. The cytoplasmic clarity in atypical basal cells, architectural disorder with cell aggregates or nest-like structures within the epidermis often cause challenge particularly in sun-damaged skin. The aim of this review is to evaluate the effectiveness of the most often used immunohistochemical melanocyte markers in the diagnosis of intraepidermal lesions. All the analyzed markers can be useful in detection of intraepidermal melanocytes that occur more densely in lentigo maligna than in solar lentigo or sun-damaged skin. However, the number of these cells is underestimated by HMB-45 and Mel-5. The cytoplasmic Melan-A staining may overestimate melanocyte number and highlight the dendritic process. Atypical melanized keratinocytes in actinic keratoses and nest-like structures in lichenoid dermatoses may mimic atypical melanocytes in melanomas in situ. S-100 remains a marker of high sensitivity but low specificity. The nuclear localization of MITF, SOX-10, and PRAME overcomes the problem of melanosome transfer to cells of other types. Neither MITF nor SOX-10 is detectable in keratinocytes, which makes them useful in distinguishing actinic keratoses from melanomas in situ. The use of markers considered as melanocyte specific suggests that lichenoid dermatoses constitute a heterogeneous group of lesions.