A mutant human epidermal growth factor receptor (EGFR) cDNA with a T-to-G nucleotide substitution in exon 21 that replaces leucine with arginine at amino acid position 858 (L858R) was cloned between a tetracycline-responsive element and an intron and polyadenylation signal from the mouse protamine 1 gene. Mice with this transgene that express the tetracycline transactivator (tTA) or reverse transactivator (rtTA) protein under the control of a tissue-specific promoter can be induced to express the mutant EGFR in tissues or cell types of interest by administration/withdrawal of doxycycline.