Case Number : Case 2040 - 30 March 2018 Posted By: Dr. Richard Carr

Extrammary paget's. 

Can't tell if there are dermal lesional nests or not.

There is a lot of acantholysis. Also, in the last pic, the nest of malignant cells lies directly on the basement membrane whereas Paget's cells are supposed to lie above the basal keratinocytes and 'crush' them.These two points raise the possibility of Pagetoid SCC and melanoma. CK7 and S100 should clarify. EMPD of course remains the third differential diagnosis.

The multiple locations of these lesions do not favor SCC or melanoma.

Syringocystadenocarcinoma papilliferum with a predominant in situ component, pagetoid. 

My first impression was also extramammary Paget's. What about ck7, ck20 and p63?

I like Vincenzo diagnosis of syringocystadenocarcinoma papilliferum in situ with pagetoid spread. The differential diagnosis would be extramammary Paget's disease with syringocystadenocarcinoma papilliferum in situ-like changes. I think it's definitely very difficult to differentiate the two entities from each other. But considering the history of "large erosive painful plaque of vulva, perineum, pubis, inguinal folds", I have to say this is most likely extramammary Paget's disease with syringocystadenocarcinoma papilliferum in situ-like changes.

A reference is included:

Syringocystadenocarcinoma Papilliferum In Situ-Like Changes in Extramammary Paget Disease: A Report of 11 Cases.

The report quoted above says that the native basal cell layer was intact. But here, the malignant cells seem to lie directly on the basement membrane.

This was a nice example of acantholytic extra-mammary Paget's. Nice discussion. Thanks.

Amazing!