Bracken fern, phenacetin, and cancer of the urinary tract.

Bracken fern, a forage contaminant, is causally related to urinary bladder cancer in animals. In this review of experimental studies on carcinogenesis of bracken fern, little evidence of an association between cancer and bracken fern in humans was observed. Clinicoepidemiological studies have shown a high frequency of phenacetin abusers in certain cases of lower urinary tract cancers that indicate case-control studies of phenacetin and related compounds are needed.