A 4-cm mass in the right kidney of a 43-year-old female had an endocri
ne appearance by light microscopy and electron microscopy confirmed th
is impression, demonstrating the presence of numerous cytoplasmic gran
ules of endocrine caliber. Unusual features were patchy immunoreactivi
ty for chromogranin, and polarity of the granules within the neoplasti
c cells. Extrarenal extension and liver metastasis were documented.