[Fibrosarcoma in onocytoma (author's transl)].

In a 69-year-old male patient a leftsided renal tumor was found. The patient who initially refused an operation, was treated surgically 3 1/2 years later, when loss of strength and weight as well as pain in the upper abdomen were noted. The tumorweight was 920 g and represented histologically, besides a oncocytic adenoma, a fibrous sarcoma. Both tumors were intermingled. We assume that the malignant growth originated in degenerated areas of the benign adenoma.