NTP workshop: animal models for the NTP rodent cancer bioassay: stocks and strains--should we switch?

The National Toxicology Program (NTP) hosted a workshop, "Animal Models for the NTP Rodent Cancer Bioassay: Strains and Stocks--Should We Switch?" on June 16-17, 2005, at the National Institute of Environmental Health Sciences (NIEHS) in Research Triangle Park, North Carolina. The workshop's objectives were to determine (1) whether the currently used models, the F344/N rat and B6C3F1/N mouse, continue to be appropriate to identify substances that may pose a carcinogenic hazard for humans and (2) whether the NTP should consider conducting cancer bioassays using multiple strains of rats and/or mice to better capture the range of genetic variability. Workshop participants advised the NTP to discontinue using the current F344/N strain due to the recent issues with fertility, seizure activity, and chylothorax and provided several options on how the program should approach identifying and selecting a new rat model. Participants believed that the B6C3F1/N mouse is still appropriate for use by the NTP, but suggested the NTP take steps to better understand and address increases in background rates of liver tumors in this strain. Finally, the participants supported the NTP exploring the use of the multiple strain approach, although they raised many questions concerning data interpretation and feasibility. This article also outlines the NTP's next steps in pursuing the workshop recommendations.