Case Number : Case 2233 - 3 January 2019 Posted By: Raul Perret

Amyloid tumor

Extraskeletal myxoid chondrosarcoma. The tumor cells are arranged in classic strings, cords, and lace-like structures with prominent myxoid stroma.

It looks like a bone biopsy with permeative growth of chondroid (atypical) tissue...agre with chondrosarcoma ( low/intermediate grade ).

Not and easy one for me. But, after read the comments, i agree that the morphology is consistent whit a Extraskeletal Myxoid Chondrosarcoma as Henry proposed.

Ok! Myoepithelioma could be a viable alternative, but S100 is almost always positive in myxoid ch. and a faint EMA-positivity shouldn't rule out this diagnosis...Sincerly this EMA positivity is more then faint, but nevertheless I still favor Chondrosarcoma.

...a vague, unclear nested pattern fit well ME, but...too vague!

Great comments! Indeed, this was a textbook example of extraeskeletal myxoid chondrosarcoma. RT-PCR showed an EWSR1-NR4A3 fusion transcript confirming the diagnosis. Despite the deceiving morphology  with delicate cells lacking atypia, these tumors are highly aggressive sarcomas. The disposition in small cords and circular patterns is very suggestive of this entity. In addition, the presence of hemorrhage with hemosiderin deposition is another good clue. Necrotic areas are also frequent. As you guys suggested, the main differential is myoepithelioma which can show morphological and immunophenotypic overlap. In this setting sox10 is a good marker as it tends to be positive in most myoepitheliomas and negative in EMC. Have a wonderful day