P-glycoprotein expression predicts response to chemotherapy in previously untreated advanced breast cancer

This study was undertaken to define the role of P-glycoprotein (P-glyc), as a marker of multidrug resistance (MDR) and to determine if it would predict both response to chemotherapy and prognosis in 42 previously untreated patients with advanced breast carcinoma. P-glyc was assayed using the monoclonal antibody (Mab) JSB-1 using an immunocytochemical method. On the same tumours, the following biological features were also estimated: tumour angiogenesis, epidermal growth factor receptor, c-erbB-2 oncoprotein and growth fraction using immunohistochemistry with immunocytochemically factor VIII-related antigen, EGFR1 Mab, 21N antibody and Ki-67 Mab, respectively. Overall, 50% of carcinomas were JSB-1 positive and the presence of P-glyc was not significantly associated with any other factor, but it was significantly predictive of poor response with anthracycline based chemotherapy (p=0.03). Moreover, lack of initial response to chemotherapy was significantly correlated with the percentage of cells staining with the JSB-1 antibody (p=0.016). P-glyc expression and the proportion of cells staining as JSB-1 positive correlated with clinical stage and analysis showed that they significantly predicted response to chemotherapy only in stage IV patients (p=0.015 and p