Case Number : Case 1995 - 29 Jan 2018 Posted By: Limin Yu

Intraepidermal malignant epithelioid lesion with a pagetoid spreading appearance. In the vulva the differential diagnosis of course lies between Paget's disease and melanoma in situ. The last two pictures appear to show pigment in the cytoplasm of the neoplastic cells suggestive of melanoma in situ. But the first three show significantly more pagetoid spread in the upper layer of the epidermis relative to malignant cells arranged in solitary units along the basal layer and no obvious nests of malignant cells along the basal layer (as commonly seen in melanoma). In figure 3 I think I see the single malignant cells lying above underlying keratinocytes instead of directly on the basement membrane as in melanoma. So overall the lesion most likely represent Paget's disease. In my practice, if I need to confirm it, I usually order only cytokeratin 7.

Agree with the above. Third DD is Pagetoid SCC in situ.

Agree with above 

Thank you for the insightful discussion and comprehensive differential diagnosis!  This is an extramammary Paget's disease, confirmed by immunostains. 

Lovely EMPD