Light micrograph of a renal oncocytoma. A renal oncocytoma is a benign tumour that occurs in the kidney. It has cells with abundant eosinophilic (pink) cytoplasm and round uniform nuclei (dark blue dots). Often, the oncocytoma cells form nests or collections of cells within oedematous stroma (light pink to white background). Haematoxylin and eosin stained tissue section. Magnification: x200 when printed at 10cm.