Case Number : Case 3037 - 25 February 2022 Posted By: Dr. Richard Carr

Two distinct population of melanocytes- junctional cells look Spitzoid, dermal cells are banal. Whether this is just a combined nevus or some kind of recurrence phenomenon in the context of previous sunburn... can't decide.

EDIT: IHC updated, loss of p16 and positive PRAME in the intraepidermal component seem to point to MIS and a dermal nevus

I don’t know if it make sense calling this dysplastic nevus, but lamellar concentric fibrosis around rete ridge and a mild random atypia fit well the classic dysplastic nevus description. Anyway this is a nevus, for me. Am’I wrong?

On H&E alone was thinking more in terms of dysplastic nevus. Melan A does not show significant pagetoid spread, but there is loss of p16 and PRAME is expressed in epidermal component, although only on one  image difficult to say if it is above threshold of >75% cells. Tough one to choose between dysplastic nevus or early MIS.  

It is interesting to see the quite different p16 in the bland dermal naevus and the junctional proliferation. Also agree I'd probably have signed out many lesions such as this as dysplastic naevus especially at this age. The PRAME is positive (4+, >75% of nuclei) so we favoured a melanoma in situ arising in a pre-existing naevus. Of course quite subjective how you approach these lesions but good to ensure complete excision with clear margins.