Rodent tumors of urinary bladder, renal cortex, and thyroid gland in IARC Monographs evaluations of carcinogenic risk to humans

Abstract

2of carcinogenicity in experimental animals as if they presented a carcinogenic risk to humans. However, the possibility that an agent causes cancer in animals through a mechanism that does not operate in humans must be taken into account. During recent years, evidence has developed that certain neoplasms, commonly seen in bioassays for carcinogenicity in rodents, can, in some cases, develop through such mechanisms. These neoplasms include urinary bladder carcinomas associated with urolithiasis, microcrystalluria, and certain urinary precipitates; renal cortical neoplasms arising specifically in male rats in association with a-2 urinary globulin (a2u) nephropathy; and thyroid follicular-cell tumors associated with imbalances in thyroid stimulating hormone (TSH) levels. All of these conditions involve persistent hyperplasia in specific cell types from which neoplasms arise. Tumors can arise in all three organ sites in rodents, in response to exposure to various clearly genotoxic carcinogens, but histologically similar neoplasms also may develop in response to certain nongenotoxic agents. To consider how rodent tumors of the urinary bladder, renal cortex, and thyroid gland should be treated within the IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, a scientific advisory group