Case Number : Case 2767 - 12 February 2021 Posted By: Dr. Richard Carr

Inverted Follicular Keratosis. 

I think it´s a KeratoAcanthoma with some features of regression.

KA like SCC

It looks like an IFK, but a DT, also. 

How about after IHC?

Proliferating Trichilemmal Cyst. 

Entrapped collagen. Wild type p53 50% peripheral. P16 checker board peripheral. Ki67 very active in the infiltrate part. Well circumscribed and above sweat coils. Scary looking cells but I think another vote for KA. 

For me P53 and P16 are wild type. So I favor KA

I´m not sure about the Ki67 it seems high but i maybe it´s limited to the basal part of the lesion.

I have struggled with this one.  I'm not sure if the first image is through the middle of the lesion, and others at the edge which would potentially affect the cell proliferation patterns.  I scored this at 8/34 which is in the equivocal range between definite KA and fSCC.  I'm still  not confident at interpreting the p16/53 and Ki67 patterns.  I'm sitting on the fence!

p53 and p16 wild type. Crateriform squamoproliferative lesion with well-differentiated glassy cytoplasm, with entrapped elastic fibres at the base. Could we call this a KA?

Okay great discussion. I found this one incredibly difficult so we all agree on this. My score: Symmetry, Lateral lips, Crater, Rounded Base, Verticality, Depth relative to sweat glands, dyskeratosis / parakeratosis, necrosis, mucin, lichenoid reaction, stromal desmoplasia all zero; thickened basaloid periperies, maturation, acantholysis all 0.5; regression 1; neurtophils microabscesses: 2 i.e. 4.5/32. For me I really was not sure if this was a KA or a follicular SCC, I don't expect this amount of clear cut elastic/collagen entrapment in IFK / SEBK with KA-like features or other benign eruptive verrucous keratosis. The location could be compatible with either diagnosis although certainly rapid growth and realtively young age are supportive of KA. The IHC I interpreted as showing no clear-cut aberration, p16 and p53 both highly compatible with KA. So I suspect this is an early KA but had to admit some uncertainty in my report (KAL SPLUMP) but thought it carried a low risk (as discussed in our MDM). UK guidelines have recently been up-dated for SCC and would make this a pT1 "low risk" if called an SCC and patient would not require follow-up in secondary care (I did not think there was enough clear cut evidence to call it an SCC though). I believe we should admit uncertainty in diagnosis rather than push everything in to a dichotomous classification which is not real life. You may ask why I'm no longer scoring entrapment - well we found it was not particularly critical and so I'm only doing EVG in cases where the differential includes reactive pseudoepitheliomatous hyperplasia v's invasive lesion (KA or invasive SCC). It appears some KA do have very circumscript borders without entrapment (although this is not so common) - this case illustrated is more typical for KA being highly infiltrative but of course FSCC can also be highly infiltrative even when showing good maturation resembling a KA (so I've stopped doing the EVG routinely after my audit findings).

Glad to have good company in the Vacillators' Club!

I think we have to be confident about a don't know! We cannot predict the future (i.e. whether a lesion will or will not behave in a way unexpected by us) and should therefore admit we cannot be perfect so while I'm >95% confident this patient will come to no harm I'm not 100%! I don't think if we are <5% uncertain for malignancy we should call or indeed necessarily manage the lesion as cancer which seems to be increasingly afflicting the challenging melanocytic cases I review. We should be able to explain we favour a benign "outcome" without necessarily being certain of a diagnosis and not strung up if our "educated guesses" occasionally proved incorrect - assuming we've not made a blatant error in which case we should hold our hands up and say I think I got this one wrong.

3 hours ago, Dr. Richard Carr said:

I think we have to be confident about a don't know! We cannot predict the future (i.e. whether a lesion will or will not behave in a way unexpected by us) and should therefore admit we cannot be perfect so while I'm >95% confident this patient will come to no harm I'm not 100%! I don't think if we are <5% uncertain for malignancy we should call or indeed necessarily manage the lesion as cancer which seems to be increasingly afflicting the challenging melanocytic cases I review. We should be able to explain we favour a benign "outcome" without necessarily being certain of a diagnosis and not strung up if our "educated guesses" occasionally proved incorrect - assuming we've not made a blatant error in which case we should hold our hands up and say I think I got this one wrong.

Totally agree!!!

Beautiful case. Thanks for sharing. I thought KA on H&e but as you say IHC was hard to decipher.

Totally agree With the approach