Fig. 1

Macroscopic findings and histological and immunohistochemical findings of the low-grade oncocytic tumor: A: Macroscopic appearance of the resected tumor of the right kidney (partial nephrectomy). The tumor, 10 mm in diameter, was located beneath the renal capsule and is indicated with arrows. The tumor was solid and tan. B: Hematoxylin and eosin (HE)-stained section showing the boundary (arrows) between the tumor and the nontumorous kidney. There was no fibrous capsule at the boundary. The tumor cells showed solid growth pattern. (Original magnification x20). C: Microscopic appearance of the tumor. The tumor was composed of oncocytic tumor cells. The tumor cells formed tight trabecular or small glands in the area showing solid growth patten. (HE section, original magnification x200). D: Higher magnification image of the tumor. Tumor cells exhibited round nuclei. Some cells show a few inconspicuous nucleoli. A few tumor cells showed a vague perinuclear halo (arrows). (HE section, original magnification x600). E: Edematous area of the tumor. The area was located in the center of the tumor. The tumor cells formed irregular glands. Some tumor cells were scattered individually, and myoepithelial cell–like cells with small nuclei and scant cytoplasm were scattered in the stroma. (HE section, original magnification x100). F: Immunohistochemical staining of KRT7. All tumor cells strongly expressed KRT7. (Original magnification x20). G: Immunohistochemical staining of KIT. The tumor cells were diffusely negative for KIT (original magnification x20). Inset image shows KIT-negative tumor cells (original magnification x200)