Functional analysis of lapatinib-resistant HER2 mutation K753E in HER2-positive breast cancer...Trastuzumab and lapatinib treatment significantly decreased the number of colonies formed by MCF10A cells bearing HER2 L768S or V773L mutation but did not significantly reduce the number of colonies formed by MCF10A cells with HER2 K753E mutation...Meanwhile, neither drug was able to significantly reduce the number of colonies formed by MCF10A cells with HER2 K753E mutation, indicating that K753E was resistant to these drug.