Case Number : Case 2238 - 10 January 2019 Posted By: Raul Perret

Spindle Cell Lipoma

DFSP.

Agree. Didn´t cross my mind at the initial evaluation but yes, the Myxoid variant of the DFSP is a good differential.

Probably the size and the "superficial" location make me still favored SCL

Waiting for the brown stains and more comments to keep learning

Spindle cell lipoma (SCL). Besides good location,  histology of fat and bland spindle cells proliferation, there are still some identifiable "ropey" collagen bundles seen in picture 1. Overall, the clinical presentation and histological features are most in favor of SCL.

What do you guys think now? 

More interesting.

Probably I still need Rb1 IHQ (I dont know if there is a "cd34 negative SCL") but if Rb1 is retained let me add to the differential: Cellular Angiolipoma.

4 hours ago, Raul Perret said:

What do you guys think now? 

 Now, I am not so in favor of SCL given the negative CD34.... how about S100 and EMA stain?

S100 and ema not performed. Rb1 negative

Atypical Spindle Cell Lipomatous Tumor???...I never view ( NEVER DIAGNOSED ) before...and should be a dedifferentiated type...

SFT with fat? or a WD-Liposarcoma.

The adipocytes are very round and whit variation in size so Im gonna favor a WD-Liposarcoma

23 hours ago, Raul Perret said:

 

 Thank you Raul, a brilliant case! 

So what's is this? SFT? WD/DD-Liposarcoma? SCL?

My spot, after IHC, is liposarcoma( dedifferentiated). Sometimes LS is STAT6 positive. 

 This was a tricky case of lipomatous/fat-forming solitary fibrous tumor. The difficulty in this case lies in the clinical context and the histology which points towards a spindle cell lipoma. Nevertheless, the irregularity of the nuclei and the prominent ramified vessels are not typically seen in SCL. In addition, the lack of cd34 expression goes strongly against this diagnosis. Another important point is to perform the highly specific stat6 when morphology is compatible with SFT, even if cd34 is negative (5-10% of SFTs). As you guys correctly suggested, the possibility of a dedifferentiated liposarcoma  with expression of STAT6 has to be ruled out. Even though superficially located liposarcomas are exceptional, this possibility was not favoured due to the lack of expression of MDM2 and HMGA2. 

Wow!

A big Wow!