The clinical success of gefitinib, an inhibitor of EGFR, in a subset of lung cancers harboring activating mutations within the kinase domain of EGFR led to the investigation of analogous mutations of ERBB2. ERBB2 kinase domain mutations were found to occur in 2–4% of lung adenocarcinomas (Stephens et al., 2004; Shigematsu et al., 2005; Buttitta et al., 2006) and cause increased survival, invasiveness, and tumorigenicity in cell-based transformation assays (Wang et al., 2006). The gene discussed is EGFR; the disease is lung adenocarcinoma.