Thus, the tumor size in the lapatinib-treated MMTV-HER2/MMTV-MED1 group is similar to that of the vehicle-treated MMTV-HER2 control group and is significantly larger than that of the lapatinib-treated MMTV-HER2 group at the time of tumor collection (Figure 5B). This evidence concerns the gene ERBB2 and neoplasm.