Gender differences in the incidence of background and chemically induced primary pulmonary neoplasms in B6C3F1 mice: a retrospective analysis of the National Toxicology Program (NTP) carcinogenicity bioassays.

The National Toxicology Program (NTP) database of technical reports on carcinogenicity bioassays has been interrogated for the incidence of primary pulmonary neoplasms in B6C3F1 mice. A total of 170 study reports were selected, from studies that completed the in-life phase during 1983-2007, which included neoplasm incidence data for 180 control groups comprising both male and female mice. The incidence (median and inter-quartile range) of males with alveolar/bronchiolar adenoma was 16% (12-20%), and for females it was 5% (2-8%); the incidence of males with alveolar/bronchiolar carcinoma was 8% (4-12%), and for females it was 2% (0-4%); and the incidence of males with combined alveolar/bronchiolar adenoma or carcinoma was 24% (18-30%), and for females it was 8% (6-12%). Comparing the incidence of animals bearing these lesions on a per study basis showed the median incidence in males to be 3.0-fold, 2.0-fold, and 2.8-fold higher than in females. The incidence of other primary pulmonary neoplasms was <10% of the alveolar/bronchiolar neoplasms. Comparison of gender-specific response to lung tumorigens showed that the increase in incidence of tumors above control levels was greater in females than in males.