Case Number : Case 2792- 19 March 2021 Posted By: Dr. Richard Carr

The clinical morphology, age and site would favour KA.  Applying Dr. Carr's scoring system (case 2707  20th November 2020) I scored it 9/32, which is below the threshold for suspecting a follicular SCC. - so it's a KA for me.

This lesion was removed relatively early.  I think it's likely that the histology, and therefore the grading score would change if it had been left a little longer.  For example, the keratinous core tends to expand with time, and thereby the lateral lips and the crater might become more obvious.  Other histological changes are likely to be time-sensitive as well.

My score = 26% ( 9/17 ). However agree with Richard’s comment. Probably this lesion was removed early. So I think this lesion would fit a KA diagnosis. 

Errata corrige: (9/34). 

KA for me also

KA for me too

Agree. KA for me too.

Well Differentiated SCC

KA.

KA?

Apologies for delay I'm on hols for a couple of weeks. On seeing these images I agree with Richard L. and colleagues who favour a KA. I'll check my database on Tuesday when I'm back in work but it looks as though you've pretty much nailed this case as a likely early KA in which the inflammatory response, for some reason, is somewhat deficient. It raises the question does KA regress because of the immune system or is the immune system reaction "incidental". I've always thought the latter is most likely and that KA's regress because they are following the hair follicle cycle akin to pilomatrixoma - they terminally differentiate and go in to "catagen" and are therefore essentially benign in the pure form. Although malignant transformation may and does occur I suspect this is uncommon (<5%) of KA. Most lesions reported as KA with malignant transformation I suspect to be KA-like follicular SCC from the outset (this currently anecdotal evidence is supported by my reading of the IHC in 100s of cases now). It also brings in to question whether KA are more or less dangerous in the immunocompromised - again there is a lack of evidence because of historical mis-diagnosis and the answers will require better studies based on more reliable diagnosis and now with IHC support. However my current gut feeling is that KA are not more aggressive in the immunocompromised.

The clinical, most of the H&E and IHC in particular in the above case is typical for KA. I can't say what the scaly patch was but it's not uncommon to see KA develop in association with over lesions (including SEBK/Solar lentigo, actinic keratosis etc. etc.).

We hope to move all these KA themed cases into a separate location on the site and I'll go back to a wider range of material in the near future but I hope you have appreciated going in depth into this challenging areas and have found it useful to you - I certainly appreciate critical (positive or negative) feedback on my cases and whether you are happy to see more cases in this theme. Warm regards Richard.

I scored this case as 5/34 (neutrophil microabscess 2; Lichenoid reaciton 2; Regression 1 and 0 for everything else), i.e. 14.7% or KA favoured by score but by intuition and gut I thought it was a KA and it's nice the IHC appears to support that designation. So I think we can say in KA you don't always see a prominent inflammatory reaction in early lesions.

Thanks Richard for this interestiing case. I hope you keep posting such cases, although I do beleive that KA is one presentation of well-differentiated SCC and its behaviour depends on the immunity of the patient.