Case Number : Case 2055 - 23 April 2018 Posted By: Raul Perret

Difficult lesion without immunostains. Architecturally looks nested in a myxoid/ chondroid stroma. Cytologically probably best descibed as epithelioid, maybe a little bit spindle. Definitely need immunos. Assuming this is a primary tumor soft tissue and not a metastasis and it is superficial, I would like to rule out a myoepithelial lesion first. But it is quite big. Tough case.

Spindle and stellate cells in abundant myxoid stroma. Some cells probably have intracellular mucin. I think this is a low grade myxofibrosarcoma

A myxoid superficial tumor, with some myxochondroid features and some hypercromatic nucleus...my first spot is Extraskeletal Myxoid Chondrosarcoma. But this is challenging case. 

Let me add another spot: Myxoid Solitary Fibrous Tumor...because of branched, staghorn vessels. 

Are there lipoblasts in the high power image? could it be myxoid liposarcoma?

Myxoid DFSP

This is S-100, what do you guys think about?

Ossifying fibromyxoid tumor ( without bone tissue )-

OFMT was my first impression, but without bone component and without IHC it was difficult to   support. 

Myxoid malignant melanoma? It is supposed to be a 'malicious masquerade' according to one paper and stromal cells secrete mucin.

This was a case of myxoid liposarcoma confirmed by the presence of DDIT3 rearrangement on FISH analysis. I was starting my training in soft tissues when I examined this case and my first hypothesis was low grade myxofibrosarcoma as some of you guys mentioned. I subsequently showed the case to my mentor Jean Michel Coindre and he instantly told me it was myxoid LPS to confirm by FISH.

Morphologically, what we see here is a proliferation of cells with inconspicuous cytoplasm and round to oval hyperchromatic nuclei surounded by an abundant myxoid matrix rich in small anastomosed capillaries. From my point of view the difficulty in this case is caused by two aspects:

A) The cellularity is increased compared to classic myxoid liposarcomas, this is typically seen in what is known as "transitional areas" which are an considered by some authors as an intermediate stage between "classic myxoid LPS" and "high grade (round cell) myxoid liposarcoma". Another explanation for the increased cellularity is that biopsy may have been performed at the periphery of the tumor which is usually more cellular (zonation phenomenon).

B) Nuclear atypia is somewhat a bit more prominent (at least to my eyes) to what we usually expect in myxoid LPS.

For the diagnosis of this entity we usually are based on morphology and we search directly a DDIT3 rearrangement by FISH (present in more than 95% of cases). In addition, this tumor frequently shows s-100 positivity (at least focally) and a vascular marker like cd31/cd34 can help to remark the typical vasculature in difficult cases.

Thank you very much for your comments, and congrats to Mona who arrived to the correct diagnosis!

Very interesting case.

The superficial location, the vascular pattern (more dilated than the common chicken-wire vascular pattern commonly seen in myxoid liposarcoma), and the lack of any identifiable lipoblasts at the periphery is unusual for myxoid liposarcoma. But nowadays molecular study trumps morphology.