HISTORY: 61 yrs old female with rectal tumor with suspition of GIST was biopsied. Our diagnosis was: "sarcoma, most probably clear cell sarcoma vs MPNST". Wide resection eith anus was performed (photo attached).  
HISTO: Vague nodules of epithelioid and spindle cells with expansive border, spreading in mucosa, muscular wall, vaginal wall. Histologically seems "melanoma like": with focal hialynised areas, focal necrosis. Metastases in 3/30 perirectal nodes are present!  
IH: S100(+/++) 70%, Vimentin (+++) 100%, Asm Actin(-), PanCK(-)(single cells <5%+), Melan A/HMB45(-), EMA(-), CD117(-)(mastocytes +), Desmin(-), CD34(-)(neovascularity +), Ki67 50% (++), Cam5.2/CK7/CK19(-), CD57(-)(T lymphos +), CD56(+) 30%, NSE(+/+++) 70%, ER(-), CD31(+)(10% (meybr phoning), CD21/CD23/CD1a(-).  
MOLECS: EWSR break FISH in progress. Any fixed/known traslocations t(12;22) ir t(2;22) for clear cell sarcoma absent. BRAF mutation absent. C-kit ex9/11/13/17 mutations absent.  
 
PROPOSAL: Clear cell sarcoma (no translocations; S100+; HMB/Melan A(-)) vs MPNST (epithelioid)(S100+; CD56+; CD57(-)).  
Thank you for beeing together.

tzankov 2011-07-18 12:55	Dear Ugnius,     a difficult case. Considering the morphology with spindly and oval cells with some cytoplasmic clearance, the dense hyalinizaion and the compartmentalizing fibrosis as well as the phenotype and the presence of lymph node metastases, I think that the tumor best fits to clear cell sarcoma except for the lacking translocations. Thogether with Dr. Frank, we do not think that this is a MPNST. An SMA/Actin and the CD99 stainig should be done and should remain negative, while Mel-CAM (CD146) might be positive and should be done as well. For principal purposes I would suggest to stain the case also for DOG1.
ugnius 2011-07-18 14:14	Thank you. CD99 only possible at the moment. EWSR1 break in progress...
ugnius 2011-07-19 16:26	Please find CD99 (focal, faint, noisy, maybe nonspecific). EWSR break in progress...
asif45 2011-07-23 07:36	I agree, morphologically this looks like a clear cell sarcoma, however immunohistochemistry (HMB45-, Melan A-) sortof goes against this. very rare cases of MPNST with mets to lymph nodes have been reported in the literature (http://www.ijcep.com/files/IJCEP1008002.pdf). I believe EWSR1 break would hold the key.     Thanks   Asif Loya
ugnius 2011-07-28 13:08	Unfortunately EWSR1 break detected onlu in minor population about 9 percent, so we have no definite argue for CCS. Anyway, I agree that CSS diagnosis is most probable. Thank you all involved in Dx.
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