I regret the poor quality of the slides.  
My problem: obviously a mesenchymal tumor forming osteoid, bone and cartilage, but in my opinion the cells look bland. Few/no mitotic figures. Is this a benign tumor or a sarcoma ? Thanks for your opinion !

I favor an ossifying fibromyxoid tumor of soft parts as a tumor of the intermediate group. It consists of hypocellular fibromyxoid parts and of cellular areas with bland small epitheloid cells. The formation of trabecular bone is characteristic and a focal cartilaginous differentiation is also compatible with this rare tumor entity.

I absolutely agree in favoring ossifying fibromyxoid tumor (OFT) of soft tissue as the primary differential diagnosis. The amount of osteoid formation seems to be too much for extraskeletal myxoid chondrosarcoma and also the cells do not seem very eosinophilic. In any case, the tumor should be completely resected and the patient should be kept in routine follow ups since OFTs can occasionally recur and metastasize. For future cases it would be very helpful to get some kind of radiologic documentation of the cases.