Atypical renal adenocarcinoma with features suggesting collecting duct origin and mimicking a mucinous adenocarcinoma

We report a case of an atypical renal adenocarcinoma of the renal medulla associated with a marked desmoplastic response and interstitial mucin production. Collecting duct epithelium of the renal medulla throughout the kidney showed cytologic atypia. These features have been described by others as suggestive of a collecting duct histogenesis. This case represents the fifteenth reported case known to us of a renal adenocarcinoma of collecting duct origin. Prior reports, however, have not described the extensive mucin production that may be associated.