Case Number : Case 2676 - 08 October 2020 Posted By: Saleem Taibjee

Epithelioid fibrous histiocytoma with mucinous cells.

Expansile upper dermal tumour, forming a sessile polyp with epidermal collarette.  Cells have a sheeted, epithelioid pattern without storiform arrangement.  Cytology is both granular and mucinous, also showing pigment granules in places, more likely haemosiderin than melanin.  Agree with epithelioid fibrous histiocytoma.  Expect ALK1 +ve and S100 -ve.

Agree!!!

agree

S100 stain below:

LCH? Not found any eosinophil! CD1a?

Here is the CD1a and Langerin:

LCH incognito?!

I think the Langerhans cells contribute only a small cellular component of the lesion. IHC with Cyclin D1 would be interesting because reactive Langerhans cells are supposed to be negative for Cyclin D1 whereas neoplastic Langerhans cells are positive for Cyclin D1. I think at least ALK-1 and CKAE/AE3 are needed to classify this lesion.

3 hours ago, anh said:

I think the Langerhans cells contribute only a small cellular component of the lesion. IHC with Cyclin D1 would be interesting because reactive Langerhans cells are supposed to be negative for Cyclin D1 whereas neoplastic Langerhans cells are positive for Cyclin D1. I think at least ALK-1 and CKAE/AE3 are needed to classify this lesion.

Agree. 

Yes, you are all very good, this is epithelioid fibrous histiocytoma.

The ALK (shown below) is strikingly positive.

The ‘mucinous cells’ in this case are rather striking. I see this term/morphology described in Kazakov et al. Am J Dermatopathol 2018;40:805-14. However, I wonder if it is better regarded as a xanthomatization, especially since some of the cells resemble Touton cells and there is expression of histiocytic markers e.g. CD163 below.

As you have alluded to, there are genuine Langerhans cells within the infiltrate, but these are a minority and a ‘red herring’.

I find this rather fascinating. In discussions about Epithelioid FH, there are uncertainties about histogenesis. But for me this case provides evidence of a true histiocytic lineage, and a further illustration of the histiocytic plasticity which is recognised in other entities such as indeterminate histiocytosis. One could infer that the presence of Langerhans cells are a further manifestation of this plasticity, or alternatively present as reactive background cells.

Of course, EFH is readily recognisable if one is familiar with the diagnosis. But to highlight that ‘“One only sees what one looks for. One only looks for what one knows.” ― Goethe, this particular case was initially misdiagnosed as malignant melanoma by the referring hospital team, prior to sending to me for second opinion.

Fascinating.  Thank you Saleem.