A Reexamination of Liver Tumors in Mice Exposed to Wholly Vaporized Unleaded Gasoline

Abstract

A single lifetime inhalation study of the effects of wholly vaporized unleaded gasoline has been conducted in the mouse. An elevation of hepatocellular tumors was reported only in females and only at the high treatment level (2056 ppm). Several reports of this study have appeared previously in the scientific literature, including a comprehensive summary published in this journal. Different incidence rates were reported for mouse liver tumors in these publications without explanations of how they were calculated of why they differed. To clarify the data, we recently examined the final report of the gasoline study, the individual animal data, and slides prepared from liver tissue collected during the study. The previously reported incidence rates did not take into consideration all animals at risk for tumor development or all animals with hepatocellular tumors. Revised incidence rates are presented for hepatocellular tumors in all mice on study. These rates are approximately 20–25% lower than previously reported.