To test this hypothesis, we studied the impact of trastuzumab plus lapatinib delivered to patients with HER2+ breast cancer on i) CSC biomarkers (CD44v and ALDH1) in tumor tissues, ii) EMT markers (TWIST1, SNAIL1, SLUG, ZEB1, and FOXC2) in CTCs in peripheral blood, and iii) the ratios of phosphorylated to phosphorylated EGFR (pEGFR/EGFR), HER2 (pHER2/HER2), ERK (pERK/ERK), and Akt (pAkt/Akt) in tumor tissues. The gene discussed is ERBB2; the disease is breast cancer.