ERBB2 and breast cancer: Our early studies showed that co-expression of erbB2 and erbB3 in human breast cancer cell lines induced activation of PI-3 K/Akt signaling and was associated with an increased resistance to multiple chemotherapeutic agents, such as paclitaxel, doxorubicin, 5-fluorouracil, etoposide, and camptothecin [60].