The Effect of Human Influenza Virus (Type A) on the Incidence of Lung Tumors in Mice^*

The carcinogenicity of human influenza virus (type A, PR-8 strain) for lung tumors was studied in mice. The infection produced great, tumor-like, epithelial hyperplasia during the recovery stage. Some influenza-induced lung lesions persisted throughout the life of the animals. These changes did not eventuate in lung tumor in mice of the low lung tumor strain C57 black. Neither was the infection carcinogenic nor the epithelial hyperplasia precancerous in the high spontaneous lung tumor strain A as judged by (a) no increase in the number of mice with tumor, (b) no increase in the average number of tumors per tumor mouse, (c) no greater number of tumors arising from influenzal lesions than from noninfluenzal areas, (d) no reduction in the tumor induction time, and (e) no visible microscopic transformation of influenza-induced hyperplasia to tumor.

There was a suggestion that the influenza infection might have been anticarcinogenic as indicated by a lower per cent yield of tumors (in one experiment), and a lengthening of the tumor induction time (in two experiments) in the virus-infected as compared with the unexposed control mice.