Case Number : Case 2651 - 03 September 2020 Posted By: Saleem Taibjee

It could be atypical fibroxanthoma clear cell variant, but needs IHC to rule out more common differential Dx 

At a glance: balloon cell melanoma.

Growth pattern, nested type, ---> Ballon Cell Melanoma; but cytological details ( nuclear indentation by cytoplasmic vacuoles ) ---> histiocytic/lipomatous/sebaceous tumor, for example AFX, balloon cell type, but also Clear Cell Renal Cell Carcinoma.It needs CPC and IHC.

First thought, Balloon cell melanoma!

Quote

At a glance: balloon cell melanoma.

Growth pattern, nested type, ---> Ballon Cell Melanoma; but cytological details ( nuclear indentation by cytoplasmic vacuoles ) ---> histiocytic/lipomatous/sebaceous tumor, for example AFX, balloon cell type, but also Clear Cell Renal Cell Carcinoma.It needs CPC and IHC.

Totally agree. I recall a case with similar features here: https://dermpathpro.com/spot-diagnosis-1/free-spot-diagnosis-december-2014/september-2017/case-1899-07-sept-dr-richard-carr-r1956/

Clear Cell Atypical Fibroxanthoma DD  Balloon cell melanoma

IHC and CPC is needed

Balloon cell melanoma

A selection of the immunos attached.

AFX Clear/Ballon cell variant (after seen the IHCs)

Yes, this is a clear cell variant of AFX. The cytology is quite beautiful. I included the p53 above just to highlight that I have found p53 very helpful over the years in AFX / pleomorphic dermal sarcoma, not only in diagnosis but in determining margins (especially in re-excision specimen in distinguishing between scar). Most cases are mutated in my experience, mostly upregulated, but this was an example of a null. 

It is really quite amazing how similar the morphology is to Richard's previous case of balloon cell melanoma which was quoted above, and shows how dependent we are upon immunohistochemistry.

Very interesting case Dr Saleem.

Just for the record the case cited above was actually a Metastasic Renal Cell Carcinoma

Thanks, Alex.