ERBB2 (V777L) mutation and ERBB2 overexpression has been shown to be sensitive to lapatinib in biliary tract cancer, breast cancer cell lines and other isogenic systems overexpressing the alteration.18, 39 Functional studies performed using gallbladder cell lines establish that ERBB2 and EGFR are essential for the survival of gallbladder cancer cells. Here, ERBB2 is linked to breast cancer.