Papillary adenoma of the kidney with mucinous secretion.

Although infrequently, mucin secretion has previously been reported in papillary renal cell carcinoma. We here investigate the presence of mucin in a series of 93 renal papillary adenomas in 58 patients. Acid mucin was present in four cases (4.3% of the tumors; 6.9% of the patients), in which basophilic mucin secretion was evident with hematoxylin-eosin. To the best of our knowledge mucin secretion has not been reported in renal papillary adenoma. We describe two different types of mucin secretion: intracytoplasmic and luminal. The secretion was intracellular in numerous scattered tumor cells in two cases, focal luminal in one case, and mixed intracellular and luminal in another case. Mucin production, despite its low frequency, can be considered as an additional feature of renal papillary adenoma. Mucin production suggests that renal papillary adenoma and papillary renal cell carcinoma are actually not two independent biological processes, but a continuum of one biological process.