The average amount of tumors harvested at 4-week time point after the first tumor appearance was significantly decreased in bitransgenic mice from all three strains (MMTV-neu, 8.61+/−2.8 g (n = 10) vs. 3.48+/−1.32 g (n = 6, p = 0.0010) for strain 76; 3.08+/−1.08 g (n = 11, p<0.0001) for strain 79; 3.63+/−2.89 g, (n = 9, p = 0.0014) for strain 138) (Fig. 6A). This evidence concerns the gene ERBB2 and neoplasm.