ERBB2 and endometrial cancer: Lapatinib inhibited the proliferation of all endometrial cancer cell lines investigated in a concentration-dependent fashion; however, the IC50 values varied significantly between individual cell lines with up to a 200-fold difference in the IC50 values and ranged between 0.052 μM in HER2-overexpressing USPC2 endometrial cancer cells and 10.9 μM in MFE296 cells that express low levels of HER2 and EGFR (Table 1).