Immunohistochemistry for identification of neoplasic cells within brisk infiltrate of thin melanomas

Thin melanomas are frequently associated with brisk lymphocytic infiltrate. Pigmented melanocytes are difficult to distinguish from melanophages, which are usually seen interspersed among lymphocytes on routine hematoxylin and eosin (HE) stained slides. As the presence of melanocytes in the papillary dermis characterizes the lesion as Clark II requiring the Breslow index, it is important to identify these cells properly and overcome such technical limitations. Even using immunohistochemistry staining for Melan-A and DAB as chromogens, this distinction is still difficult because the brown pigment formed by the chromogen DBA can not be easily differentiated from the brown melanin granules. We have introduced a simple modification on the technique, by replacing hematoxylin with Giemsa as counterstain. In this regard, the melanin pigment was decorated in green-blue while the Melan-A positive melanocytes were colored brown. Negatively stained melanophages contain only course green-blue granules of melanin in their cytoplasm. Thus, we were able to identify Melan-A positive cells in the papillary dermis accurately, determining microinvasion (Clark II) in 31 (77,5%) out of 40 in situ (Clark I) melanomas associated with brisk infiltrate. This technique is useful to distinguish melanophages and melanocytes interspersed among the lymphocytic infiltrate associated to thin melanomas, allowing detection of early invasion and avoiding Clark levels and Breslow index misinterpretation.

Thin melanomas; In situ melanomas; Melan-A; Immunohistochemistry

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