Immunohistochemistry of pigmented actinic keratoses, actinic keratoses, melanomas in situ and solar lentigines with Melan-A

Distinguishing lentigo maligna from solar lentigo, and pigmented actinic keratosis can sometimes be problematic. Melan-A is an immunohistochemical marker which that can be helpful in decorating the melanocytes of pigmented lesions. A recent report has suggested that Melan-A may spuriously label nests of junctional keratinocytes, potentially leading to the misdiagnosis of melanoma in situ. We compared Melan-A immunohistochemical staining in pigmented actinic keratosis, non-pigmented actinic keratoses, melanoma in situ of lentigo maligna type and solar lentigines. We found a statistically significant increase of Melan-A staining in melanoma in situ, but no statistical difference in the number of junctional Melan-A positively staining cells, in solar lentigines, pigmented actinic keratoses, and non-pigmented actinic keratoses, respectively. In the non non-melanoma samples, the Melan-A A-positive cells located at the dermal-epidermal junction were interspersed and not observed in clusters. Increased staining with Melan-A, in an actinic keratosis, or solar lentigo should raise the possibility of a contiguous melanoma in situ.