ERBB2 and breast cancer: The combination of HLX22 and HLX02 also led to strong synergistic inhibitory effects on BT-474 breast cancer cell proliferation with combination indices ranging from 0.081 to 0.046 (strong synergy, Fig. 3f, i, j), as well as on SKRB3 breast cancer cell proliferation (3 + HER2 expression, Fig. 3g).