Clinical history: Skin lesion in a 60 year old woman.
What is the differential and favored diagnosis on H+E? what immunostains would clarify the diagnosis?
The histologic appearance on H&E consists of marked cellular atypia centered along the dermal-epidermal junction. There is an associated inflammatory response. On H&E it may be difficult to distinguish this entity from melanoma, and in areas the atypia extends high into the epidermis, which may lead to confusion with Bowen's disease. In this specimen many of the cells contain melanin, highlighted with the Melanin-A stain. The tumor cells are negative for S-100 however, and positive for AE1/3, along with the associated normal keratinocytes, eliminating melanoma from the differential. CK7 is positive, differentiating the tumor from surrounding keratinocytes and removing Bowen's disease from the differential. The CK7 stain also nicely illustrates the pagetoid spread of tumor cells within the epidermis.