60 yrs female underwent tumor resection from duodeno-jejunal junction muscular wall.  
MACRO: 14 cm small intestine with circumscribed, lobated, broght borwn 6,5x3x6 cm tumor.  
HISTO: Biphasic tumor in muscularis propria, well circumscribed, with lobation/spetation with small infiltrative nidus closed to main mass. 1 zone: Castlemann like areas with follicles with FDC whorls and interfollicular atypical spindle cell spread; 2 zone- more aggressive, epithelioid solid and spindled cell tumor. Mitoses ~6/10 HPF. In tumor periphery (subserosa), sinuses still present (lymph node spread).  
Original diagnosis: Malignant mesenchymal tumor, most probably GIST with high malignant potential): CD117 (-)(sic!), CD34/ASMACTIN/DESMIN/S-100(-); VIMENTIN (+).  
REVIEW AND EXPANDED IH in 2009 under request of GIST registry as CD117 negative GIST.  
IH SUMMARY: VIMENTIN+, CD68+ (epithelioid), CD23-/+ (single cells in epithelioid), CD21+, PanCK(-), EMA+. ALK1/DESMIN/CD34/CD117/CD20/CD3/EBV LMP1/AsmACTIN(-). Ki67 highest in epithelioid cell component ~ 40%.  
VIRTUAL SLIDES: Pending.  
PROPOSAL: Jejunal folicullar dendritic cell sarcoma (with epithelioid (high grade) and Castlemann/IMFT like (low grade) areas).  
 
SPECIAL QUEST: Castlemann lymphadenopathy like tumor component with interfollicular interstitial tumor cell population, histo and IH different (CD68-/+; CD21/CD23/S100-) from main epithelioid tumor mass (CD68+; CD21+; CD23-/+; S100-): unclassifiable dendritic cell component? FDC component IMFT like?.  
 
Series of these 2 cases are dedicated to Basel hematopathology team. It's pleasure be with you on the web.