Case Number : Case 2537 - 27 March 2020 Posted By: Dr. Richard Carr

Not melanoma for me. DPN could be a good spot. 

intradermal nevus with atypia

Predominantly cytoplasmic stain of P16, chessboard pattern, should be consistent with nevus, but I don't know much about this intriguing pathological chapter of IHC.

Difficult to characterize. Does not appear overtly melanoma. Superficial variant of deep penetrating nevus or blitz nevus (combined spitz+Blue), intradermal spitzoid nevus or MELTUMP

I've asked for the Cyclin D1 to be posted. Sorry I don't have beta-catenin available!

Case c/o Dr Iqbal Dhesi.

My report: Many thanks for sending this challenging melanocytic lesion.  We have an overwhelmingly dermal proliferation of slightly enlarged melanocytes with accompanying melanophages scattered through the lesion.  The lesion forms interstitial clusters and small theques. Cellular pleomorphism is mild. Two mitotic figures are noted in only one of the multiple cross sections.  The lesion has a slight wedge-shape down growth surrounding an adnexal structure. There is a lack of maturation with depth. Immunohistochemistry is quite helpful.  S100 diffusely positive rules out blue naevus.  Ki67 shows low proliferation fraction.  Melan A is diffusely positive through the lesion and shows only a slight increase in dendritic melanocytes along the basal layer of the epidermis, of doubtful significance. In my opinion this is a deep penetrating type naevus.  This diagnosis is supported by the presence of prominent site nuclear cyclin D1 evenly distributed throughout the lesion.  

Deep penetrating naevi generally have nuclear expression of Beta-catenin.  Most lesions are combined and occur as phenotypic heterogeneity within a pre-existing naevocellular naevus although I could not identify a pre-existing naevus in your case.  Lesions are challenging for diagnosis and given that the tumour cells abut the radial margin of this biopsy, a modest re-excision of 3 -5 mm around the biopsy site would be recommended.  Malignant transformation is rare.