Case Number : Case 3076 - 21 April 2022 Posted By: Saleem Taibjee

BAP1-inactivated melanocytic tumor.

Spitzoid morphology, BAPoma is a good thought. No atypical junctional component, more or less symmetrical on low power, no significant mitotic activity or atypia from the pictures. 

Agree with BAPOMA

Looks like Spitz nevus. I cannot distinguish any type of combined nevus. Do you know if it is a RET fusion?

I don’t see bapoma-like cells, but it’s a my impression of course. There are spitzoid features, (NTRK3?). If BRAFV600E neg favor a SN. I know many pathologists prefer the AST label for these cases.  But it looks like benign  for me. 

The additional relevant IHC is shown below. ALK showed some positive staining which might suggest an underlying driver ALK fusion, p16 appears lost, Ki67 low. Not shown, but BAP-1 was preserved, ROS-1 and NTRK negative.

This type of IHC is constituting my 'Spitz' IHC panel in these difficult sorts of lesions.

In this case, with the loss of p16, I erred towards 'atypical Spitz tumour', and advised MDT discussion + aiming for re-excision. One could also consider ancillary investigations such as FISH.

BW
Saleem