Helicobacter hepaticus (H. hepaticus)
infection causes
hepatitis and increased hepatocellular
neoplasms in male mice; although females are also infected, liver lesions are not typically expressed. In the 1990s, B6C3F1 mice from some chronic National Toxicology Program (NTP) studies were found to be infected with H. hepaticus. In these studies, there was
hepatitis in many of the males, and there were more hepatocellular
neoplasms in control males compared to studies with uninfected mice. In one of these studies, increased hepatocellular
neoplasms at the high doses in male and female mice exposed topically to
triethanolamine (
TEA) provided the only evidence of carcinogenic activity. This study was repeated in mice free of H. hepaticus.However, the NTP mouse production colony and the diet differed between studies; these differences were the result of NTP programmatic decisions. In repeat study males, although control incidences were similar between studies, exposure did not result in increased hepatocellular
neoplasms. In repeat study females, the control incidence of hepatocellular
neoplasms was half that observed in the initial study, and these
neoplasms were increased over controls at all doses. These data suggest that in the initial study, H. hepaticusinfluenced the induction of hepatocellular
neoplasms in males, but not in females.