1. A transgenic mouse whose genome comprises a Jaagsiekte sheep retrovirus (JSRV) envelope protein (Env)-encoding transgene operably linked to a surfactant protein C promoter (SPCp), wherein the lung tissue of the transgenic mouse expresses the transgene, and wherein the transgenic mouse is characterized by having more than 5% of chance to develop a lung tumor by the age of 1 month, or having more than 8% of chance to develop a lung tumor by the age of 3 months, or having more than 20% of chance to develop a lung tumor by the age of 7 months, and further wherein the transgenic mouse has an FVB/N genetic background.