Correlation of phosphorylated HER2 with clinicopathological characteristics and efficacy of trastuzumab treatment for breast cancer.

Aim: To determine the correlation of phosphotylated human epidermal growth factor receptor-2 (pHER2) with clinicopathological characteristics of breast cancer (BC) and patients' response to trastuzumab-based therapy. Patients and Methods: pHER2 was determinated immuno-histochemically in 88 cases of HER2-positive and 50 cases of HER2-negative BC. All patients with HER2-positive BC received trastuzumab-based therapy and 16 of them (18.2%) had disease progression during therapy treatment (i.e. trastuzumab-resistant). Results: pHER2 was predominantly expressed in HER2-positive BC, with 55 cases (62.5%) of tumours expressing pHER2. Six cases of HER2-negative cancer (12.5%) displayed positive expression of pHER2. Expression of pHER2 correlated with younger age of patients and negative oestrogen receptor status. Acquisition of resistance to trastuzumab correlated with negativity for pHER2 (p=0.028). Conclusion: Positive expression of pHER2 may yield additional information regarding the poor prognosis of BC and could be used for pre-selection of patients with HER2-overexpressing BC displaying resistance to trastuzumab treatment.