Rodent bladder tumors do not always predict for humans

Area of Science:

• Toxicology and Carcinogenesis
• Urology and Nephrology

Background:

• Dr. David Clayson's 20-year-old hypothesis questioned the relevance of rodent urinary calculi to human cancer risk.
• Urinary calculi, microcrystalluria, and amorphous precipitates complicate the interpretation of rodent bioassays.

Purpose of the Study:

• To review the role of urinary calculi in bladder carcinogenesis over the past 20 years.
• To assess the impact of solid urinary materials on extrapolating rodent carcinogenicity data to humans.

Main Methods:

• Literature review of studies on urinary calculi and bladder cancer in rodents.
• Analysis of examples illustrating the formation and effects of urinary precipitates.
• Examination of the mechanism of action for non-genotoxic chemicals causing calculi.

Main Results:

• Chemicals inducing urinary calculi in rodents are non-genotoxic.
• These substances promote cancer through increased cell proliferation, not direct DNA damage.
• Calculi formation presents an artifactual concern for human carcinogenic risk extrapolation.

Conclusions:

• The formation of urinary calculi and precipitates in rodents is a significant artifact in carcinogenicity studies.
• The non-genotoxic mechanism involving cell proliferation highlights challenges in human risk assessment.
• Further research is needed to refine the extrapolation of rodent bioassay findings to human health.