Case Number : Case 2717 - 04 December 2020 Posted By: Dr. Richard Carr

It's obvious that folk are reluctant to comment on this lesion.  Clinically it would do very well for a keratoacanthoma, and it's on the intermittently sun-exposed skin of a limb.

However, applying Richard Carr's KA/fSCC histological scoring system to this lesion (see case 2707 posted 20.11.20) I assessed this lesion as scoring 12/34, which is the reported threshold for a diagnosis of follicular SCC.  So that is what I will call it, and if I'm wrong it is not entirely my fault!

Wow! 

I have also attempted to score this based on list of Criteria given by Dr. Carr. I got 14/32 (instead of 34, as I could not evaluate for elastic trapping in the absence of EVG. So, I would go for follicular SCC in this one. 

20 minutes ago, Meenakshi Batrani said:

I have also attempted to score this based on list of Criteria given by Dr. Carr. I got 14/32 (instead of 34, as I could not evaluate for elastic trapping in the absence of EVG. So, I would go for follicular SCC in this one. 

Yes, you are correct.  I should therefore amend my score to 12/32 in the absence of EVG - still enough for a diagnosis of fSCC.

Strictly speaking you'd struggle to assess features that relate to the base, verticality, depth below sweat gland coils etc. I think you can assess the crater, lips, and many of the other features. That said you have similar scores!!!!

Not enough familiar with Richard’s score system, for now; but I’m learning little by little. I’d like favor KA...

Still learning Richard’s system. Being on methotrexate, lack of pushing border in this squamoproliferative lesion, I would favour a follicular SCC over a KA.

My score is 10/34. 

Sym:1, lat lips:1, crater:0, base:0, lateral:0, depth:0, dysk/parak:2, intraepith n:2, necrosis:0, basaloid per:0, matur:0, acantholysis:0, mucin:0, lich reaction:2, desm:0, regression:2, elastic:0. 

Tell me what I’m going wrong. 

I take Richard's point about the difficulty in assessing some of the features in this superficial biopsy.  Perhaps we shouldn't apply the criteria in this situation.

From a clinical perspective, the patient has a history of non-melanoma skin cancer and is on methotrexate.  Therefore, regardless of the final histological diagnosis, this has to be considered a higher risk lesion which requires wider excision.

atypical squamoproliferative lesion and follicular SCC cannot be ruled out complete excision suggested

severely sun-damaged skin, acantholysis and null p16 makes me think it is SCC

Symmetry n/a; Lateral lips: 1; Crater: 1; Base, Depth to SG, n/a; Dyskeratosis / parakeratosis: 1.5; N. microabscesses: 1.5; Necrosis: 0; Basaloid peripheries: 0; Maturation: 0; Acantholysis: 0.5; Mucin: 0; Lichenoid reaction: 1.5; Stromal desmoplasia: 0; Regression 1.5; Entrapment (EVG): 0; = 8.5/26 = 32.7% (i.e. FSCC favoured). The scoring is very provisional and a "rough guide" helps us remember to assess all the criteria. The patient has extensive erythrodermic psoriasis and in all probability has had PUVA and is on methotrexate. So I expect this is not usual non-sun-exposed skin. Several images we see acantholytic changes in the mature keratinocytes (in the abscence of neutrophils this is NOT a feature of KA and on it's own is highly disturbing).

The IHC shows a clear cut mutant pattern for p16 (weak "wishy washy" mainly cytoplasmic peripheral pattern). p53  is wild type and importantly closely correlates (when wild) with Ki67 (peripheral only). Well diff. to Mod. Diff. SCC, follicular type (typical tricholemmal pattern of keratinisation with plump glassy keratinocytes) is the the final favoured diagnosis (definitely NOT a typical KA). A proportion of FSCC closely mimic the clinical features of KA and the histological ones. In my opinion they explain the vast bulk of so-called metastasising KA or KA with malignant transformation that have been reported in the literature. Sad to say but even Weedon who would regularly make a diagnosis of KA on 2mm punch biopsies was blissfully unaware of the nuanced diagnostic features that distinguish FSCC KA-like from KA.

Follicular SCC KA-like are all infundibular-tricholemmal tumours and have yet to make their mark on the WHO classification of cutaneous skin tumours despite being seen weekly if not daily in sign-out (if your cases are biased to SCC and melanoma like my cases). However if you live in the UK, the RCPath datasets describe the features in some detail. 

New information on EVG - it does not help! Some typical solitary KA are completely circumscript with no entrapment and others vary greatly in the extent of entrapment. Ditto for FSCC. So we can start to assess 16 features although as you've realised we can add in the points about extent of sun-exposed skin etc.

Hoping to submit our IHC paper before christmas and will have to hold our fingers crossed the reviewers don't reject!

Warm regards to all

R