Immunohistochemical analysis of P-glycoprotein expression in breast cancer: clinical correlations

Paraffin-embedded, formalin-fixed tissue (PEFFT) specimens from a subset of breast cancer patients were analyzed by immunohistochemistry to determine whether or not the presence of P-glycoprotein identified chemotherapy resistance. Two antibodies, C219 (monoclonal) and Ab1 (polyclonal), demonstrated appropriate immunostaining. Retrospectively and prospectively, P-glycoprotein expression was determined from PEFFT of 20 breast cancer biopsies (19 patients with locally advanced or metastatic disease). Immunohistochemical staining was graded for number of positive cells (N0 to N4) and intensity (I0 to I3). The immunostaining N and I of both antibodies were similar. There was no correlation between N, (P = 0.13) or I, (P = 0.67) and chemotherapy response or between N, (P = 0.63) or I, (P = 0.89) and survival. Five patients had residual cancer at repeat biopsy after systemic chemotherapy for locally advanced disease. These specimens had similar N and I as the primary cancer. This assay accurately identifies P-glycoprotein expression in PEFFT and revealed no correlation between expression and chemotherapy response or survival.