Spontaneous regression of renal cell carcinoma: a pitfall in diagnosis of renal lesions.

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Abstract
Two cases of renal cell carcinoma, both of which underwent extensive spontaneous regression, are reported. The first occurred in a 56 year old man, forming a well circumscribed renal cortical nodule which contained only very occasional foci of viable renal cell carcinoma with areas of hyalinisation and calcification, and with metaplastic ossification. The second lesion was removed from an 82 year old man, comprising a cystic cavity containing necrotic debris with only occasional viable foci of classical renal cell carcinoma. Spontaneous regression of renal cell carcinoma is a rare but recognised entity. These two cases emphasise the important differential diagnoses: metastatic secondary carcinomas, xanthogranulomatous pyelonephritis, and infective granulomatous conditions of the kidney. The importance of adequate tissue sampling of all renal nodules cannot be overemphasised in the processing for examination of lesions within the kidney.