Case Number : CT0067 Adam_Bates

Great-sized cells with abundant foamy eosinophilic cytoplasm. The nuclei are large and pleomorphic, showing oval or cleaved outlines. Nucleoli are prominent. An atypical mitotic figure can be found. I won’t hesitate calling this a malignant tumor. Immunohistochemical study suggests histiocytic sarcoma.
 

Agree , malignant hisiocytosis/histiocytic sarcoma. pleomorphic foamy histiocytes with prominant nucleoli & atypical mitoses. few eosinophils

This appears to be a histiocytic lesion with granular cell change. I would also include infection, foreign body reaction and benign neoplasms such as granular cell dermatofibroma in the differential. 

Agree with histiocytic sarcoma. Though the cells are large, I would also consider myeloid sarcoma with monoblastic differentiation, and follicular dendritic cell sarcoma as an H&E Differential diagnosis.
 

I perceived the cells as having granular cytoplasm not foamy. Thought of primitive non neural granular cell tumor ( I know it is S100 _ve and CD68 +ve), not aware of it's CD163 positivity???. It contain vesicular nuclei, small prominent nucleoli with some scattered atypia and mitoses,,, Also thought of granular cell dendrocytosis... I might however be out of the track !!!!!!!!!!!!!!
 

My first thought was an S100 - granular cell tumor. I just don't see enough atypia to call this a histiocytic sarcoma. The cytoplasm is very granular, the nuclei while mildly atypical are not that pleomorphic, and the mitotic rate appears actually fairly low. I'd be surprised if this was malignant.
 

For the CD163 and after some reading, I would suggest also the following DD: Granular cell variant of epithelioid cell histiocytoma...
 

This was called non-neural (S-100 negative) malignant granular cell tumor.
 

gree with Dr Mona: Granular cell variant of epithelioid cell histiocytoma.
And also: non-neural granular cell tumor.
I wouldn't call it malignant, as those lesions can have many mitosis and prominent nucleoli.

An interesting and rare case!

The high-grade cytology is very similar to that seen in the S100+ granular cell tumor that was posted this week for expert review in the 'DIFFICULT OPINION CASES' area