Molecular analysis of RTK signaling in BT474 and SKBR3 ErbB2+ breast cancer cells indicated that the combination of lapatinib with low-dose ganetespib (50 nM) enhances the inhibition of ErbB2, Akt, Erk1/2, mTOR, and GSK3 activation/phosphorylation. The gene discussed is MAPK3; the disease is breast carcinoma.