Rare renal tumor--mucinous tubular and spindle cell carcinoma.

We report a rare case of renal tumor--mucinous tubular and spindle cell carcinoma in a 65-year-old man. The tumor, located in the right kidney, was well circumscribed. Microscopically, the tumoral proliferation was composed of cuboidal cells arranged in tubules, with abrupt transition to spindle cell morphology in a myxoid stroma. Because of the favorable prognosis with this type of tumor, mucinous tubular and spindle cell carcinoma must be differentiated from papillary renal cell carcinoma, especially the variant with sarcomatoid dedifferentiation.