HER2/HER3 co-overexpression is significantly associated with impaired OS from diagnosis of metastatic disease in patients with HER2-positive metastatic breast cancer.     ///    Co-inhibition of HER2 and HER3 or the inhibition of HER2/HER3 hetero-dimerization may improve clinical outcome in this subgroup..     ///    Co-overexpression of HER2/HER3 is a predictor of impaired survival in breast cancer patients..     ///    HER2/HER3 co-overexpression was observed in 12/110 (11%) specimens and HER3-overexpression showed a statistically significant association with HER2-overexpression (p = 0.02). 