Case Number : Case 1942 - 08 Nov Posted By: Iskander H. Chaudhry

Spitz nevus. Depending upon age, mitoses, ki67 measured prolif rate, HMB45 stratification,  and p16 expression, it could be classified as atypical spitz nevus or spitz tumor. I would go out on the limb and predict ALK1 overexpression! 

Not completely excised, so recommend excision to ensure complete  removal and examine the base.

Dear all - The age and gender have now been added!. Jen, Admin

Eh, just saw it on big screen. Melanoma.

Not an easy lesion. There are some worrisome features like dense cellularity, irregular nesting, pseudomaturation? Would check for mitoses, perform ki67, HMB45, Melan-A and p16. I am worried about nevoid melanoma 

Worrisome features. Expansive growth pattern. Mitosis and atypical cytological features (pic4). Difficult because there is deep maturation like a nevus. I think this is a spitzoid melanoma. But the important is complete removal and sentinel lymphadenectomy, and also a full stadiation. 

Melanoma

worried about this one.... the cellular expansile nests are concerning and I think there are mitoses  (image 6). Would go for melanoma (Spitzoid or naevoid, whatever one wants to call it)

I favor melanoma specially in this age,sun exposed area ,dermal mitoses and junctional cells.

Ki67 is more than spot distribution in dermal component. HMB45 + in deep dermal component. ALK neg as expected ( it’s usually positive in only 2-4% primitive melanomas ). So melanoma seems a correct diagnosis. 

Naevoid melanoma

Impossible for me! i.e. a MELTUMP. Comments below are heavily influenced by Dr Arnoud de la Fouchardiere who gave most excellent talks in Oxford at our recent National Skin External Quality Assurance scheme.  It seems to be a moving field!

DDx:

Atypical Spitz category. Gene fusion cases can have less clear cut Spitzoid morphology. I wondered if it could be an NTRK1 lesion. MET, ROS1 are others (ALK seems excluded).

Non-Spitzoid: Rarely you can get spindle/spitzoid morphology in mutated NRAS amplification lesions (NRAS excludes Spitz group).

I suppose can it be a developing spindle cell melanoma (needs BRAF, molecular work-up including CGH).

Atypical cellular or Malignant blue (probably less likely - but look for a subtle pre-existing blue (G proteins & +/- BAP loss).

Arnoud de la Fouchardiere showed as amazing examples of clear cell sarcomas that very closely mimicked melanocytic lesions (in fact they probably are melanocytic but with distinct molecular genetics EWSR break apart) that included cases with junctioanal component.

As you can see a little bit of knowledge can be a bad thing!

Dear All 

Dr Chaudhry's final comments:

The lesion was considered too expansile to be benign in a person of this age. The junctional portion is limited, but does include atypical cells and does not have an ordered naevoid architecture(nests but also individual cells, some suprabasal); there are sparse but definite suprabasal melanocytes elsewhere, too. There was no problem finding mitoses, including some at least mid-dermis. 

The final diagnosis was:

Spindle cell melanocytic neoplasm, favour malignant, FISH should be considered. Wide excision advised.