Case Number : Case 1792 - 11 April - Dr Uma Sundram Posted By: Guest

Dr Uma Sundram has an infectious case for you all today, enjoy.

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Melanoma insitu

Yes, agree with Mona! Melanoma in situ! There was some concern in fig 2 because of busy dermis, but I think it's an inflammatory reaction, so favour an "intraepidermal lesion"!

Odd history and site for melanoma. Did you see melanin?

Tought of Paget's when I saw the case and the weird location

Looks like an in-situ melanoma with some regression in the dermis. Agree with Richard's comment regarding 'odd -site'. IHC to rule out an odd extramammary Paget's (although the pattern of spread along the epidermis  is a bit odd).

Agree with above comments, and I thought of Paget too, but a junctional and nested arrangement like this, instead a "pagetoid" one, would be very unusual for a Paget . The intraepidermal growth pattern seems much "melanocytic" in fig 3, 4.    IHC is mandatory of course.

Definitly EMPD is a ddx .. IHC mandatory

Difficult case!. Some cells look pagetoid?

34 minutes ago, Sasi Attili said:

Difficult case!. Some cells look pagetoid?

Yes. For me even if they grow mainly in nests, the cells have rather clear abundant cytoplasm and even in the last pic it looks like there are some with signet-ring cell like morphology

Hard to distinguish, without mucin and immunohistochemical stains, between nested extramammary Paget’s disease and nested superficial spreading melanoma in situ. I favor the former, taking into account the site (perianal region is rich in apocrine sweat glands), cytologic findings (cells have abundant pale amphophilic cytoplasm, some of them with intracytoplasmic clear droplets and signet-ring appearance), and architectural features (neoplastic nests are detached from the underlying compressed basal layer). Rule out intraepithelial spread from an internal carcinoma from sigmoid colon or rectum is also important.

Perfect. I too thought MIS at first glance, but indeed CK7 was positive and S100/MART-1 was negative, supporting extramammary Paget's disease. CK20 was negative and the patient had negative staging work up.