Navigating the Pathology Minefield: Harnessing the Value of Historical Control Data in Rodent Carcinogenicity Studies

A reliable and robust historical control database for tumors in control rodents, used in lifetime carcinogenicity bioassays, is an essential tool for laboratories conducting such studies. It provides a quality check for the concurrent control for a given study and, in the event that the concurrent control is deficient in some respect, it permits an objective comparison of the control incidences to those present in the respective treated groups. This review details the conditions where a HCD may help, the factors that need to be taken into account when constructing a quality HCD, and the numerical alternatives that should be considered when using the data. It is emphasized throughout the review that HCD should not be used in isolation to dismiss an apparent treatment-related increased tumor incidence and should never supersede a detailed "weight of evidence" evaluation in coming to any conclusion as to the result of a carcinogenicity bioassay. Finally the review briefly discusses the potential for the HCD to replace the use of a concurrent control group in such studies.