case_images: PMC11222608_01
case_images: Histomorphology of inflammatory pseudotumor-like follicular dendritic cell| sarcoma. (A) The intestinal mucosa shows infiltration by a well-circumscribed, spindle cell proliferation (4X). (B) The spindle cell proliferation shows atypical spindle cells arranged in fascicles and suggested whorls with focal storiform patterned areas (10X). (C, D) Higher magnifications show oval to spindle cells with vesicular nuclei, stippled chromatin, small, centrally placed conspicuous nucleoli, scant to moderate amounts of eosinophilic and fibrillar cytoplasm, and mostly indistinct, syncytial borders. A small proportion of the oval to spindle cells demonstrate binucleation with occasional multinucleation and nuclear pseudoinclusions. A lymphoplasmacytic infiltrate with dispersed eosinophils and rare neutrophils constitute the background (40X, 100X).
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case_images: Immunohistochemical staining was positive for CD23 and CD35 with a Ki67 proliferative index of 20%, p53 (20% of tumor cells with overexpression) and EBER positivity. Immunohistochemical staining can be seen in  Figures 1 ,  2 .
case_images: Immunophenotype of inflammatory pseudotumor-like follicular dendritic cell sarcoma. (A) Focal staining of the spindle cells by CD23 confirms the follicular dendritic cell differentiation (20X). (B) CD35 also shows focally strong staining (20X). (C) EGFR is also positive (20X). (D) EBV staining is strongly and diffuse positive, which correlates with the proposed theory of tumor derivation from EBV-infected mesenchymal cells and subsequent follicular dendritic cell pathway differentiation (20X).
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case_images: f2
case_images: Immunohistochemical staining was positive for CD23 and CD35 with a Ki67 proliferative index of 20%, p53 (20% of tumor cells with overexpression) and EBER positivity. Immunohistochemical staining can be seen in  Figures 1 ,  2 .
case_images: Clinical timeline demonstrating the location and pattern of tumor recurrence.
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case_images: The timeline of the full clinical course can be seen in  Figure 3 .
case_images: PET scans performed prior (left) to dual immune checkpoint inhibitor use and after (right) four cycles of combination ipilimumab/nivolumab. Scans demonstrate increased size and avidity of the pelvic small bowel mass after treatment.
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case_images: The PET scans before and after immune checkpoint inhibitor therapy can be seen in  Figure 4 .