Neoadjuvant Chemotherapy Induces Expression Levels of Breast Cancer Resistance Protein That Predict Disease-Free Survival in Breast Cancer

<div><p>Three main xenobiotic efflux pumps have been implicated in modulating breast cancer chemotherapy responses. These are P-glycoprotein (Pgp), Multidrug Resistance-associated Protein 1 (MRP1), and Breast Cancer Resistance Protein (BCRP). We investigated expression of these proteins in breast cancers before and after neoadjuvant chemotherapy (NAC) to determine whether their levels define response to NAC or subsequent survival. Formalin-fixed paraffin-embedded tissues were collected representing matched pairs of core biopsy (pre-NAC) and surgical specimen (post-NAC) from 45 patients with invasive ductal carcinomas. NAC regimes were anthracyclines +/− taxanes. Immunohistochemistry was performed for Pgp, MRP1 and BCRP and expression was quantified objectively using computer-aided scoring. Pgp and MRP1 were significantly up-regulated after exposure to NAC (Wilcoxon signed-rank p = 0.0024 and p<0.0001), while BCRP showed more variation in response to NAC, with frequent up- (59% of cases) and down-regulation (41%) contributing to a lack of significant difference overall. Pre-NAC expression of all markers, and post-NAC expression of Pgp and MRP1 did not correlate with NAC response or with disease-free survival (DFS). Post-NAC expression of BCRP did not correlate with NAC response, but correlated significantly with DFS (Log rank p = 0.007), with longer DFS in patients with low post-NAC BCRP expression. In multivariate Cox regression analyses, post-NAC BCRP expression levels proved to predict DFS independently of standard prognostic factors, with high expression associated with a hazard ratio of 4.04 (95% confidence interval 1.3–12.2; p = 0.013). We conclude that NAC-induced expression levels of BCRP predict survival after NAC for breast cancer, while Pgp and MRP1 expression have little predictive value.</p></div

Representative staining patterns for Pgp, MRP1 and BCRP in matched breast tumour tissues pre- and post-neoadjuvant chemotherapy.

<p>Individual expression scores for each tissue shown, using a semi-automated scoring system, were: Pgp pre, 10.6; Pgp post, 117.9; MRP1 pre, 3.2; MRP1 post, 55; BCRP pre, 64.5; BCRP post, 89.7. Scale bar: 40 µm.</p

Post-NAC expression of BCRP predicts disease-free survival.

<p>Kaplan–Meier survival analyses for disease-free survival in patient groups with tumours with high or low post-NAC expression levels of Pgp (A), MRP1 (B) or BCRP (C). Cut-off used to dichotomise expression into low and high groups (Pgp: 90; MRP1∶21; BCRP: 47) were determined by ROC curve analyses (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062766#pone.0062766.s001" target="_blank">Fig. S1</a>).</p

Clinical and pathological features of the patients.

<p>Clinical and pathological features of the patients.</p