We first conducted MTS cell growth assays to examine whether inhibition of ErbB2 by lapatinib, a reversible dual EGFR/ErbB2 tyrosine kinase inhibitor, or PD168393, which irreversibly inhibits ErbB2, can lead to growth inhibition of ErbB2-positive cancer cells, such as ErbB2-positive Calu3 lung cancer and SkBr-3 breast cancer cell lines. This evidence concerns the gene ERBB2 and breast cancer.