Case Number : Case 2901 - 19 August 2021 Posted By: Dr. Richard Carr

Intradermal melanocytic nevus with a focus of nevoid melanoma

BAPOMA. 
Nuclear Bap1 loss. And my first spot on morphology features.  

I agree BAP1 inactivate nevus, BAP1 is nuclear stain and it seems to be loss of nuclear stain

ki 67 is low and P16 is preserved, it is not a melanoma

But BAPomas have epidermal flattening with only dermal component.  I agree there is nuclear loss of BAP1

BAPOMA, will wait for Dr Carr's input

Well done for not being fooled by the cytoplasmic pattern of BAP1 staining which is uncommon (although actually quite common in mesothelioma from a little google-ing). Agree with BAPoma / MBAIT.

I suggested they enquire about the possibility of the familial syndrome.

We've seen p16 in a mainly, highly aberrant, weak cytoplasmic distribution (about 10% of SCC)  and even a case of p53 in which there was aberrant cytoplasmic staining in addition to the normal nuclear only pattern. Remarkably I've also seen a recent case of p16 (E2H6) antibody completely negative in the background internal controls (in two separate specimens from the same patient) and completely normal staining in the background internal controls for another different p16 antibody. Please look out for this as it would be a big catch to interpret the tumour as pathologically "null" when the patient has a native p16 protein which does not stain for the antibody in the expected background internal controls (melanocytes, epithelia, macrophages etc). If you do find a similar case let me know as it needs writing up.