ERBB2 and breast cancer: In this study we use genetic manipulation of capns1 in HER2+ models of breast cancer to show that calpain-1 and/or calpain-2 are involved in but not required for spontaneous tumor formation in a transgenic mouse model of HER2/NEU-driven tumorigenesis; however, capns1 knockout in established carcinoma cells effectively blocked their tumor forming capability in an orthotopic engraftment model and enhanced in vitro sensitivity to doxorubicin and lapatinib.