Review ArticleDiagnostic utility of epithelial and melanocitic markers with double sequential immunohistochemical staining in differentiating melanoma in situ from invasive melanoma

- Distinction between melanoma in situ and thin melanoma may sometimes be difficult on routine slides. This interpretation can cause pitfalls even with immunohistochemical stains.
- Double sequential immunohistochemical staining with epithelial and melanocytic markers applied to the identification of melanoma in situ and differentiation from invasive melanoma.
- The double sequential immunohistochemical staining is a very useful tool in difficult cases with isolated cells in the dermis, tissue fragmentation, dense lichenoid inflammatory infiltrates or tangential sectioning.

Identification of melanoma in situ and its distinction from invasive melanoma is important because of its significant impact on morbidity and mortality. However, this interpretation can cause pitfalls in the diagnosis even with the use of immunohistochemistry. The aim of this study is to evaluate the diagnostic utility of epithelial makers (AE1/AE3, CK5/6, and p63) combined with melanocytic markers (HMB-45, S-100, or Melan-A) using dual-color immunohistochemical staining, performed on a single slide by sequentially applying the antibodies. In this study, we show 4 cases in which examination of routine hematoxylin and eosin slides did not allow for clear-cut distinction between in situ and invasive melanoma and highlight the utility of the double-staining method. Therefore, we recommend this double-staining method with melanocytic and epithelial markers as a helpful adjunct to the diagnosis of cases with a differential diagnosis between in situ and invasive melanoma.