Expression of Yes-associated protein (YAP) in metastatic breast cancer.

The purpose of this study was to investigate the expression of Yes-associated protein (YAP) in different metastatic sites in metastatic breast cancer and to determine the clinical implications of these patterns. Immunohistochemical staining was used to investigate the expression of YAP and phospho-YAP in tissue microarrays from 122 cases of metastatic breast cancer (bone metastasis = 29, brain metastasis = 38, liver metastasis = 12, and lung metastasis = 43). The expression levels of YAP and phospho-YAP differed according to the metastatic site in metastatic breast cancer. Specifically, nuclear expression of phospho-YAP was high in brain metastasis but low in lung metastasis (P = 0.010). The effects of YAP and phospho-YAP expression on clinical outcomes were investigated by univariate analysis. This analysis showed that nuclear YAP positivity (P = 0.008) and nuclear phospho-YAP positivity (P = 0.003) were both associated with shorter overall survival. In conclusion, the level of YAP expression varies according to the metastatic site in metastatic breast cancer. Moreover, high YAP expression was correlated with poor prognosis.