Of the seven novel HER2 mutations, L768S and V773L were only detected in HER2-negative tumors, whereas K753E was found in HER2-positive disease...Xenograft experiments showed that NIH3T3 cells bearing the L768S and V773L mutations displayed more rapid growth. MCF10A, BT474, and MDA-MB-231 cells bearing the K753E mutation were resistant to lapatinib, but could be inhibited by neratinib.