Additionally, concurrent treatment of metformin with an anti-HER2 antibody (trastuzumab) synergically reduced the percentage of trastuzumab-resistant CSC/TICs in breast cancer, indicating that metformin can eradicate the trastuzumab-refractory CSC/TIC population in HER2+ breast cancer [103]. Here, ERBB2 is linked to breast carcinoma.