Case Number : Case 1466 -06 February Posted By: Guest

Desmoplastic Trichilemmoma

Agree with Mona. Invasive follicular SCC. Lovely mucin!

Yes, first thought is invasive SCC. However, the mucin is stromal rather than epithelial (the latter being a feature of Follicular SCC), so not sure about the significance.

Wondered if image 6 shows perforation of epithelium by elatic fibres?? Also some neutrophilic microabscesses. If this a rapidy growing lesion, perhaps proliferating phase of Keratoacanthoma comes in the d/d (although always difficult one to make on a small bx)

It seems that I arrived late this time. Agree with folicular SCC fits with the Warwick criteria. Just as a remark the lesión doesnt seem perfectly well circumscribed and it infiltrates with small cords of neoplastic cells, I imagine this is probable a more aggresive lesion than the ones that are perfectly well circumscribed with pushing borders...

Good remark Arti, I had the doubt with picture 6 too but I finally thought it was mucin, maybe I am wrong. Dr. Carr will illuminate us

Actually you are right, they are elastic fibers and the architecture is not the classical for follicular SCC, this fits better with proliferating KA, good job.

Hmm, yes there is stromal mucin (usually not a feature of typical follicular SCCs), but there is some intra-tumoral mucin as well. Occasional micro-abscesses also present, along with perforation of elastic fibres, features of a KA! The cytological atypia in the last two images is a bit more for KA. Difficult case!

Immunostains suggest MAC, but morphologically i would had favoured DT...Difficult for me! I'm waiting for the diagnosis. 

Invasive SCC.....

I called this a poorly differentiated squamous cell carcinoma (it may be follicular - but difficult to tell in this curettage).  The interstitial-type mucin is very rare in tumours other than BCC. I think I have only seen it once or twice previously in SCC, but I thought it made a nice contrast to last weeks case.  Immunostains are commensurate with SCC (negative BerEP4 in the basaloid cells and positive EMA even in the more basaloid cells, no glandular / luminal staining).  You are all right the mucin in follicular SCC is intra-epithelial and a useful clue to think of that diagnosis.  So far I have not observed intra-epithelial or extra-epithelial mucin in KA although intra-epithelial mucin it is not uncommonly seen in tricholemmoma, inverted follicular keratosis / seborrhoeic keratosis. There is elastic entrapment - if you check our review paper we reported that mainly in poorly differentiated subtypes of follicular SCC. Finding elastic entrapment in the mature central areas in KA is as far as I am currently aware fairly specific to KA (or infundibular psuedoepitheliomatous hyperplasia).  In this case the elastic entrapment is not in central matured areas but in the more solid basaloid infiltrative areas.  In KA we like to see full maturation (to cells with more abundant glassy cytoplasm than here) in the centre of all islands - in this biopsy I don't perceive that crucial feature.  There also appears to be foci of "spontaneous" acantholysis (i.e. not confined to neutrophil microabscess) a feature that I don't usually accept in KA.  Obviously if you are not sure you have to admit the uncertainty.  Be very wary of the tip of the iceberg effect in small biopsies (KA-like and craterifrom SCC that are superficially well differentiated) and remember KA is a clinicopathological team diagnosis in my view with many potential pitfalls. Clinically this case was not at all KA-like.  In fact this was a curettage of a crusted lesion on a patient with widespread severe actinic damage and many previously treated superficial lesions.  The lesion regrew into a 12mm nodule over the next 3 months and was finally excised with a full thickness skin graft and even then the deep margin was involved.