Low-grade oncocytic tumour of kidney (CD117-negative, cytokeratin 7-positive)

The term low-grade oncocytic tumour of kidney is an emerging entity describing CD117-negative and cytokeratin 7-positive indolent tumors with overlapping morphological features between oncocytic tumors. We present herein the case of a 77-year-old female with a 3.2-cm nodule in mid pole of the left kidney. The tumor was uniformly oncocytic with solid, compact nested and trabecular growth patterns. There was common areas of transition to central zones of stromal edema with marked tumor hypocellularity and growth in cords. Some of these areas had adjacent fresh hemorrhage. Immunohistochemistry showed strong and diffuse expression of cytokeratin 7 and negativity for cKIT/CD117. The proper use of this new diagnostic category avoids labeling such tumors as unclassified renal cell carcinoma – a broad category with different morphologic features and heterogenous prognosis.