SUSAN A. ELMORE, ANNE M. RYAN, CHARLES E. WOOD, TORRIE A. CRABBS, AND ROBERT C. SILLS National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA Pfizer Inc., Pfizer Global R&D, Groton, Connecticut, USA U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA Experimental Pathology Laboratories, Inc., Research Triangle Park, North Carolina, USA