Case Number : Case 2772 - 19 February 2021 Posted By: Dr. Richard Carr

Keratoacanthoma en plaque?

I am also more in favor of Keratoacanthoma in this one. 

p53 wild type, but p16 seems mutated. Not well circumscribed ( laterality ). Infiltrative in deep dermis. Favor fSCC. 

I'll await more opinions. 3 is not really enough. If you're viewing but not opining perhaps this gentle push will help you have a go. Remind me in a week if there are a good number of opinions.

I am in the FSCC camp. I have also tried to apply the score, and my result was 10, which would be pretty high for a KA. I might be applying it wrong, though. But practice makes perfect!

On morphology alone I would have called it Scc. I’m not happy with p16. Ki67 is reassuring though- some degree of cross cutting. P53 aberrant low.

I still favour well to mod diff SCC.

KA

My report: 

Hybrid proliferating actinic keratosis with deep follicular component.

No overt invasion.

Radial margin: 2 mm

Deep margin: 1 mm

Summary: Hybrid surface and follicular actinic keratosis. No frank invasion.

Discussion Points: Striking porokeratosis-like pattern, p16 mutant null, p53 up-regulated wild type (often p53 is more prominent reactive pattern when p16 is null). This lesion also has follicular pseudoepitheliomotous hyperplasia. I'm finding you not infrequently get hybrid surface / follicular lesions. Ki67 is peripheral only but this only reflects the differentiation in this case. You could do an EVG if you thought the lesion was genuinely invasive (I didn't do it). I also got a score of 10/34 which is in favours FSCC/SCC grouping.