Pathology requirements for two-year rodent studies II. Alternative approaches

The preceeding paper described the origin and evolution of the pathology portion of carcinogen bioassays conducted under the direction of the National Cancer Institute (NCI) and subsequently by the National Toxicology Program (NTP). Review of 277 studies conducted under the NCI/NTP protocol suggested that the present number of tissues/organs was in excess to what is needed to detect if a given chemical induces cancer in rats and/or mice. In addition, the ability of the previous protocol to detect and define non-neoplastic chemically related lesions may be inadequate. This paper describes alternative pathology protocols and proposes one that will answer the question of a given chemicals' carcinogenic potential while at the same time give superior information on non-neoplastic chemical related pathology. In addition this protocol will reduce the volume of histopathology required in most studies by over 50%.