Metanephric adenoma.

A 59-year old woman was diagnosed with a tumour in her right kidney. A nephrectomy was performed, and a 45 mm diameter tan-pink coloured tumour was found. Microscopy revealed small, dark cells in organized arrays of small round acini and tubules with glomeruloid infoldings. A diagnosis of metanephric adenoma was made. The tumour cells proved diploid on flow cytometry and immunohistochemical staining was positive for CAM 5.2 and AE-3. FISH analysis of three chromosomes did not reveal any abnormal karyotype. It is important to differentiate metanephric adenoma from renal cell carcinoma and adult Wilm's tumour, since it has a benign course.