Although ongoing clinical-translational research is required to provide evidence for the usefulness of therapeutically combining metformin with HER2-targeted therapies [107], it is worth mentioning that metformin acts synergistically with the anti-HER2 monoclonal antibody trastuzumab (HerceptinTM) to eliminate stem/progenitor cell populations in HER2-gene amplified breast carcinoma cells growing as mammospheres [108]. The gene discussed is ERBB2; the disease is breast carcinoma.