PMC7785868_01
Histopathology of bone marrow biopsy showing scattered infiltration of atypical large lymphocytes. (A) Low-power view of the bone marrow biopsy (H&E stain, x50). (B) High-power view of the atypical lymphocytes (H&E stain, x200). (C) Immunohistochemical staining of CD20-positive lymphoproliferative cells (x400). (D) EBER in situ hybridization indicating positive signals in the nuclei of background cells (x200).
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F1
Histopathological examination of the bone marrow biopsy revealed scattered infiltration of large atypical lymphocytes (Figures 1A,B). These cells were positive for CD20, CD25, and MUM1, and negative for CD3 (Figure 1C). EBER-positive lymphocytes were detected using in situ hybridization background staining (Figure 1D).
Photomicrography of the nodal biopsy. (A) Low-power view reveals effaced structure by marked infiltrate of small-to-medium-sized atypical lymphocytes with clear cytoplasm (H&E stain, x100). (B) High-power view showing polymorphous lymphoid infiltrate with high endothelial venules (H&E stain, x400). (C) Immunohistochemically, large immunoblastic lymphocytes were positive for CD20 (x400). (D) Podoplanin immunostain revealed expanded follicular dendritic cell meshwork (x400). (E) EBER in situ hybridization followed by PD-1 immunostaining showed that lymphoma cells were negative for EBER. (F) EBER in situ hybridization followed by the immunostaining of CD20 indicated positive-signal lymphocytes infiltrate indicating positive signals in the nuclei of background cells (x600).
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F2
However, histological examination of the lymph nodes showed an effaced structure with a marked increase in small-to-medium-sized atypical mononuclear cells with irregular nuclei and clear cytoplasm in a background of arborizing endothelial venules (Figures 2A,B). Immunostaining showed these atypical cells were positive for CD3 and CD4, and large immunoblastic lymphocytes scattered among the neoplastic cells were positive for CD20 (Figure 2C). Podoplanin immunostaining, a highly effective marker of follicular dendritic cells, showed an expanded follicular dendritic cell meshwork, although it was negative for CD21 (Figure 2D). PD-1-positive lymphocytes were EBER-negative, while CD20-positive background cells were EBER-positive (Figures 2E,F).