Case Number : Case 2747 - 15 January 2021 Posted By: Dr. Richard Carr

PECOMA?

My differentials are: DFSP ("clear cell variant"), Clear Cell Sarcoma and (lest likely) metastasic Renal Cell Carcinoma 

Distinctive Dermal Clear Cell Mesenchymal Neoplasm.

3 minutes ago, vincenzo said:

Distinctive Dermal Clear Cell Mesenchymal Neoplasm.

First time to know about this entity! but I think it fits well! Well done Vincenzo! 

Thanks, Mona. So, in two, we may get it right. 

Skin tumour involving mainly the reticular dermis and extending to the subcutis. Composed of sheets/packets of tumour cells with distinct cell border, abundant clear cytoplasm and vesicular nuclei with prominent nucleoli (although not much nuclear pleomorphism or mitoses). Quite vascularized. Some entrapment of collagenous fibres.

If considered primary, then I think Distinctive Dermal Clear Cell Mesenchymal Neoplasm would be a nice fit as suggested already. It seems to be mesenchymal as the name suggests but the line of differentiation is unknown. Seems in McKee's newest edition it is put under 'Clear cell fibrous histiocytoma' but mentions 'The overall architecture and morphological features are not usually typical of a fibrous histiocytoma and thus may represent an altogether unrelated tumor.'

Also agree with others that we need to exclude metastatic clear cell tumours (e.g. clear cell RCC) and other soft tissue lesions (as those listed above).

Looking forward to Richard's comment.

Balloon cell/clear cell dermatofibroma.

Pecoma -:)

Great discussion. I was not sure what to call it but sent it to Chris Fletcher with the differential diagnosis of distinctive clear cell mesenchymal tumour (it's similar morphologically to the cases illustrated in the paper) and PECOMA. Chris confirmed that based on the IHC and morphological features this was completely typical of PECOMA (I guess this case fits in to the category of clear cell myomelanocytic tumour). Tumour was diffusely NKIC3+ve (a relatively non-specific marker). I've always had a bit of a blind spot for this diagnosis so I think it's nice to see an apparently typical case! Glad some of you found it similarly challenging to myself!

11 hours ago, Dr. Richard Carr said:

Great discussion. I was not sure what to call it but sent it to Chris Fletcher with the differential diagnosis of distinctive clear cell mesenchymal tumour (it's similar morphologically to the cases illustrated in the paper) and PECOMA. Chris confirmed that based on the IHC and morphological features this was completely typical of PECOMA (I guess this case fits in to the category of clear cell myomelanocytic tumour). Tumour was diffusely NKIC3+ve (a relatively non-specific marker). I've always had a bit of a blind spot for this diagnosis so I think it's nice to see an apparently typical case! Glad some of you found it similarly challenging to myself!

Thanks for sharing such a beautiful case!

Thanks for sharing this nice case with us, Richard! 

Was this a primary tumour of skin? Seems to be quite rare with indolent behaviour:

https://pubmed.ncbi.nlm.nih.gov/28556973/

Thanks Elaine, cutaneous primary. Thanks for you recent comments.

R