case_images: PMC8187768_01
case_images: Massive accumulation of 18F-fluorodeoxyglucose into the abdominal cavity in positron emission tomography. (A) Moderate ascites and wall thickening of the jejunum and ileum were seen in contrast-enhanced computed tomography. (B) Massive accumulation of 18F-fluorodeoxyglucose was observed into the peritoneum and small bowel wall. (C) An endoscopic image of a jejunum tumor detected by double balloon-assisted enteroscopy. A whitish elevated tumor was seen in the proximal jejunum.
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case_images: Moderate ascites and wall thickening of the jejunum and ileum were detected in abdominal computed tomography (CT,  Figure 1A ). 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) showed remarkable and diffuse accumulation of FDG (SUV max 12.5) into the peritoneum and small bowel wall ( Figure 1B ). DBE detected a whitish elevated lesion with surface erosions in the proximal jejunum ( Figure 1C ).
case_images: Pathological findings of jejunal biopsy samples. (A) Jejunal biopsy samples obtained from a whitish submucosal tumor were subjected to hematoxylin and eosin (H&E) staining and immunohistochemical analyses. Atypical lymphocytes were positive for CD20, and CD79a, and BCL2 whereas those were negative for MYC. Scale bar, 40 mum. (B) Cell surface expression of Ig light chains was limited to kappa chain by flow-cytometry.
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case_images: Pathological examination using jejunum biopsy samples revealed infiltration of atypical small lymphocytes positive for CD20, CD79a and BCL2 and negative for MYC in immuno-histochemical (IHC) analyses, suggesting infiltration of atypical B cells in the jejunum ( Figure 2A ). These atypical lymphocytes were monoclonal since cell surface expression of Ig light chains was limited to kappa chain by flow-cytometry ( Figure 2B ).
case_images: Pathological findings of ascitic fluid cell block samples. Ascitic fluid cell block samples were subjected to hematoxylin and eosin (H&E) staining and immunohistochemical analyses. Neoplastic lymphocytes were positive for CD10, CD20, and CD79a whereas those were negative for CD5 and MUM1. Scale bar, 50 mum.
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case_images: H&E staining using ascitic fluid cell block showed aggregation of neoplastic lymphocytes ( Figure 3 ). These neoplastic lymphocytes were negative for CD5 and MUM1 and positive for CD10, CD20, CD79a, BCL2 and BCL6 in IHC analyses ( Figures 3  and  4 ).
case_images: Immunohistochemical analyses and fluorescence in situ hybridization of ascitic fluid cell block samples. (A) Neoplastic lymphocytes were positive for BCL2, BCL6, and MYC. The percentage of Ki-67-positive cells was 70%. Scale bar, 50 mum. (B) Ascitic fluid cells were subjected to fluorescence in situ hybridization (FISH). FISH detected formation of BCL2/IgH fusion signal (arrows, yellow color) in 99 cells among analyzed 100 cells (top). Gain of MYC signal (red color) was seen in 97 cells among analyzed 100 cells (bottom).
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case_images: These neoplastic lymphocytes were negative for CD5 and MUM1 and positive for CD10, CD20, CD79a, BCL2 and BCL6 in IHC analyses ( Figures 3  and  4 ). IHC results were consistent with FL arising from the small intestine, aggressive phenotype seen in this case was atypical for FL. In fact, the percentage of neoplastic lymphocytes positive for Ki-67 was 70% ( Figure 4A ). FL into DHL or DEL, fluorescence in situ hybridization (FISH) was performed. FISH showed BCL2/IgH fusion signal in 99 cells among total 100 cells examined ( Figure 4B ). Extra copies of MYC ( Figure 4B ) were observed in 97 cells among total 100 cells examined ( Figure 4B ), suggesting that neoplastic lymphocytes were characterized by over-expression of BCL2 and MYC. In line with FISH results, overexpression of MYC was seen in IHC analyses ( Figure 4 ).