Case Number : Case 2952 - 29 October 2021 Posted By: Dr. Richard Carr

The melanocytic lesional combination of a Spitz nevus ( spindle cell type in this case ) overlying a common acquired nevus, is an unusual but well known event. I think this could be the case. 

Beta Catenin is negative. CyclinD1 mosaic pattern. I was a bit suggested by a weird junctional variant of DPN, but with this IHC…—>combined nevus. 

Challenging lesion, MELTUMP

Difficult to classify. Melanocytic nevus with atypical epithelioid component which some believe is a superficial variant of DPN or it could be a combined nevus  IDMN+Spitiz or BAP -1 inactivated tumor (but Beta catenin is not overexpressed in sptiz), MELTUMP.

Some lesions are hard to classify. I thought there was a small ordinary naevocellular naevus (nuclear beta-catenin negative, cyclinD1 low) and a rather "Spitzoid" predominantly junctional clone with some DPN-like features and indeed there is some nuclear Beta-catenin in the clone (small black arrows) to compare with the membranous only pattern in the epidermal keratinocytes (red arrows). The increased cyclinD1 fits with DPN. p16 is retained mosaic but stronger in the naevus (being a marker of cellular senescence we can see reduced expression in juncationally active lesions that are benign). The cytology is pretty bland and the PRAME negative so I thought the lesion was essentially benign and did not want raise the suspicions to a MELTUMP so my final classificatioin favours a combined naevocellular & superficial / junctional DPN clonal type naevus!