Case Number : Case 2761 - 4 February 2021 Posted By: Saleem Taibjee

A mitotically active, myxoid spindle cell tumour showing storiform patterning and monster cells.  At this age it is much more likely to be a malignant tumour than a reactive process such as nodular fasciitis. How about something rare like a myxoid liposarcoma?

Obviously immunohistochemistry is vital here.

Leiomyosarcoma ( ?metastatic ). 
Also thought of Pecoma, but too cigar shape nucleus, as expected in smooth muscle tumors. 

Tumor shows fascicles and storiform pattern with paranuclear vacuoles and cigar shaped nuclei. Above features suggest leiomyosarcoma.

Here is the pankeratin (MNF116) stain

Leiomyosarcoma

Considering the IHC, I would start thinking of something more in the lines of a sarcomatoid carcinoma, maybe even a squamous cell carcinoma.

25 minutes ago, Carmen Lisievici said:

Considering the IHC, I would start thinking of something more in the lines of a sarcomatoid carcinoma, maybe even a squamous cell carcinoma.

 

Agree.

Need p40, SMA, Desmin, S100, CD10 

Despite PanK positivity I still favor Leiomyosarcoma. Of course we need more IHC (Desmin, p40, SMA, Sox10, CD10)

OK, well done. So I didn't put you off the scent with the keratin stain. Desmin was positive (patchy), H-caldesmon strongly and diffusely positive (see below).

This was indeed metastatic leiomyosarcoma.

The case was brought to me by one of the junior pathologists in our team. My first thought on encountering the slide was to suggest to review the patient's previous medical history (it is amazing how this is frequently forgotten), and lo-and-behold it transpired that the patient was already known to Oncology with metastatic leiomyosarcoma!

Hence, I suggested a very limited initial immunopanel of pankeratin, desmin, and S100 (the latter was negative). Of course, it is interesting to see how keratin stains can be misleading, we know the pitfall that keratin can sometimes be positive in a variety of situations including melanoma, angiosarcoma. But this is the first time I have come across this with leiomyosarcoma.

BW, Saleem