ERBB2 and breast cancer: In agreement with our prior in vitro data combining [sorafenib + sildenafil + afatinib], and its effect on chaperone activity and total ERBB2 expression, in vivo in athymic mice the three drug combination of [regorafenib + sildenafil + lapatinib] profoundly suppressed BT474 mammary tumor growth to a significantly greater extent than the two drug [regorafenib + sildenafil] combination (Figure 14A, p < 0.05) [9].