Case Number : Case 2771 - 18 February 2021 Posted By: Saleem Taibjee

I think this is a peduculated, papillomatous Spitz naevus, with spindle cells predominating.

There is an interesting basophilic, tinctural alteration in the dermal collagen fibres which might be calcium deposition.  Image 4 shows small foci of black granular material which might be tattoo pigment, or calcium.

Polipoid Melanocitic lesion with some spindle and epithelioid features. I'm thinking in BAPoma. 

I would favor a Spitz nevus.

Spitz nevus .

some of the images seem to be missed off. see below

These extra view reinforce my opinion that this is a Spitz naevus.

The pigment is quite widespread in the mid dermis.  Looks more like tattoo than calcium.

It seems a bit asymmetrical, no ulceration or significant mitotic activity. I am  curious  to see P16, ki-67 and HMB45.

Alk mutated spitz nevus.

43 minutes ago, Xiao Mu said:

Alk mutated spitz nevus.

Yes, that´s a interesting option

ALK mutated SN shows usually an intradermal fascicular growth pattern. So I don’t think this is an alk mutated spitzoid lesion,  however agree with Spitz Nevus. 

There is an infiltrative growth pattern in between collagen and elastic fibers, as expected in a Nevus. Melanoma growth is usually pushing out elastic and collagen fibers. 

Hi. Thanks for the comments on this case.

Yes, I thought it was a rather fascicular Spitz lineage tumour. And there is some ALK positivity, as shown below.

I can see that there is a clear consensus for benign in the comments. I did share this case with a couple of other dermatopathologists, and in view of the rather cellular nature of the lesion, adult age group, the questionable cytological maturation (still quite epithelioid and pleomorphic at the base), we all favoured designation as Atypical Spitz (but still favouring a benign course).

Somewhat reassuringly, there is minimal mitosis, and p16 is preserved with low Ki67 and negative PRAME.

As some of you pointed out, there is tattoo pigment.

But as Richard points out in the first comment (but not really elaborated upon after that), there is this curious basophilic alteration of the collagen, as shown in the last image above. This seemed confined to the base of the tumour. I do not recall seeing anything quite like this before in the context of a melanocytic lesion, and I wonder if anyone else has? The von Kossa (not shown) is negative.

BW

Saleem

Nice!