Tumor histology. Myelomonocytic tumor cells with large round nuclei and a variable amount of cytoplasm infiltrate extensively in the left kidney, intercalating between renal tubular cells, shown via hematoxylin and eosin staining, original magnification, × 20 (A) and × 40 (B). Immunohistochemical stains using EnVision Plus from Dako (Carpinteria, CA) as the detection system with chromogen diaminobenzidine (DAB), showed that these cells were uniformly strongly positive for the proliferation marker MIB-1 (original magnification, × 40) (C). The cells were positive for myeloperoxidase (MPO), supporting their myeloid origin (original magnification, × 100). Images were visualized under an Olympus BX41 microscope equipped with an Olympus UPlan Fl 20 ×/0.50 (∞/0.17) (A), 40 ×/0.75 (∞/0.17) (B,C), or 100 ×/1.30 (oil) (D) objective lens (Olympus, Melville, NY). A U-TV 0.5 × C connector was used. Images were captured with an Olympus DP12 digital camera, digitally acquired with an Olympus UBS SmartMedia Reader-Writer, and processed with Photoshop 7.0 software (Adobe Systems, San Jose, CA).