Dermal Melanocytes Detectability for Distinguishing In Situ and Early Invasive Melanoma: A Narrative Review

The melanoma incidence has been increasing over the past three decades, with a disproportionately high fraction of in situ tumors. The diagnosis of melanoma at its earliest stages can be challenging. The detectability of tumor melanocytes in the dermis is of key importance for distinguishing in situ from invasive melanomas. In this review, a total of 475 melanomas diagnosed as in situ tumors by hematoxylin and eosin staining were analyzed. This diagnosis was confirmed for 68% of cases, but 15% of in situ melanomas were reassessed as invasive lesions using immunohistochemistry. The cases were upstaged by Melan-A/Mart-1, S-100, and SOX-10 with frequencies of 14.6%, 11.7%, and 10.8%, respectively. Whereas, the diagnosis of in situ melanoma was confirmed by SOX-10, Melan-A/Mart-1, and S-100 in 81.4%, 63.8%, and 59.1% of cases, respectively. Moreover, the analysis of immunohistochemical detectability of melanocyte markers in different types of dermal cells was carried out for 574 various skin lesions. The stainings of S-100, SOX-10, MITF, and PRAME in fibroblasts and histiocytes, as well as Melan-A/Mart-1, HMB-45, and MITF in melanophages, were noted. The diagnosis of in situ melanoma based on hematoxylin and eosin staining is confirmed by immunohistochemistry in most cases. However, some in situ tumors become reassessed as invasive malignancies. Although none of the currently used melanocyte markers is absolutely specific, simultaneous analysis of nuclear SOX-10 and cytoplasmic Melan-A/Mart-1 stainings can support the diagnosis. However, immunohistochemistry remains an auxiliary tool, and the results should be analyzed in association with the cytomorphological features.