Lymphoma and retroperitoneal fibromatosis (RF) in RRV-infected RMs. (A) Hematoxylin and eosin stain of lymphoma isolated at biopsy from the breast of animal 19185 (original magnification ×630). (B) Combined in situ hybridization of lymphoma with RRV cosmid probe (purple) and immunohistochemistry with mouse anti-CD20 (brown) and anti-CD3⁺ (gray) demonstrates that RRV is present in CD20⁺ cells comprising the lymphoma (original magnification ×630). (C) Same as panel B, except cosmid vector control replaces the RRV cosmid probe. (D) Hematoxylin and eosin stain of lymphoma isolated from liver of animal 19286 during necropsy (original magnification ×200). (E) Same as panel B, except RRV cosmid probe detected by immunofluorescence (purple) with no evidence of CD20 staining. (F) Similar to panel C; this is the control for panel E. (G) Hematoxylin and eosin stain of RF attached to the stomach of animal 18483 (original magnification ×400). (H) Combined in situ hybridization with RRV cosmid probe (purple) and immunohistochemistry with anti-CD20 (brown) and anti-CD3 (gray) shows that RRV is not present in the CD20⁺ or CD3⁺ cells (original magnification ×1000). Arrows point to RRV-positive cells that have spindle-like morphology. (I) Identical to panel H, except vector control replaces the RRV cosmid (original magnification ×630).