ERBB2 and neoplasm: In terms of tumor response outcome, although no response was observed in the chemotherapy alone groups, surprisingly, these chemotherapy regimens had the potential to induce substantial tumor response when combined with T-DM1 (62.5% for Gem/Cis+T-DM1, and 66.7% for Gem/Carbo+T-DM1). Notably, the addition of T-DM1 to the chemotherapy regimens exhibited a desirable response whereas a low level of HER2 expression was observed in both PDX models used in our study.