Case Number : Case 2701 - 12 November 2020 Posted By: Saleem Taibjee

The pleomorphic nuclear cytology, mitotic activity and collagen dissection suggest this is a malignant process.  There is no apparent connection with the epidermis, so I would go for a metastasis, especially given the anatomical location.  Immunohistochemistry needed.

A tricky maturation in this melanocytic tumor. The growth in papillary and mid dermis is expansive and stuffing. Favor melanoma. 

melanoma -nevoid type

Atypical Spitzoid melanoytic tumor, favor Melanoma. 

Hi. There seems to be general consensus that this is a worrying melanocytic lesion. In fact my bottom line histology report was almost verbatim as for Victor i.e. “Spitzoid tumour of uncertain malignant potential, but probably best managed as for melanoma”. The nests superficially are rather expansile. There was mitotic activity. However, a very good impression of maturation with depth, and no deep dermal mitoses seen. Hence I did not feel I could make a clear-cut diagnosis of melanoma based on histology alone, although I would not be at all surprised if the lesion were to metastasize.

In terms of ancillary investigations, BRAFV600E was negative, as we might expect if a true Spitz lineage. I had the impression of fascicular areas on the histology, and interestingly there was quite striking expression of ALK in this lesion, especially within these areas. This could support the possibility of an ALK fusion as a driver genetic event in this lesion, and indirectly further support Spitz lineage. As we learn more about the genetics, we realise that this in itself does not allow us to predict prognosis, because there are lesions along the whole spectrum of Spitz (Spitz naevus, STUMP, Spitz melanoma) which may have underlying ALK fusions (by the way, note that the term Spitz melanoma is now preferred to Spitzoid melanoma in this context, the latter is a morphological term which also encompasses some examples of BRAF-mutated superficial spreading melanoma which may have Spitzoid-appearing cells). See https://pubmed.ncbi.nlm.nih.gov/32701692/

Here is a nice recent review article https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6300473/

Of interest, PRAME was also positive in this lesion.

See images below.

BW

Saleem

Thanks Saleem, I learned a lot with this case.