Pathological examination. A: The gray renal tumor without capsule. B: The tumor cells exhibiting a tubulopapillary architecture. C: Hobnail-shaped cells protruding into the glandular lumen (arrow). D: The tumor cells exhibiting eosinophilic property with ill-defined bound, large and atypical nuclei, and prominent nucleoli. E: The tumor interstitial connective tissue reaction. F: Collecting duct carcinoma in situ or dysplasia (indicated by an arrow).