Molecular analysis of osteopontin and STAT3 in luminal and triple-negative/basal-like immunophenotypes of breast carcinoma.

Abstract

e11079 Background: Osteopontin (OPN) plays a role in the growth, progression and metastasis of cancer. Similarly, deregulation of the signal transducer and activator of transcription (STAT)3, a member of the Jak/STAT pathway, has been associated with neoplastic transformation. Recently, it has been suggested that OPN may regulate STAT3 signaling, leading to tumor progression and inhibition of apoptosis in breast cancer (BC) cells. Therefore, the aim of this study was to analyze OPN and STAT3 mRNA expression in a series of BC of luminal and triple-negative (TN)/basal-like immunophenotypes. Methods: We performed an immunohistochemical study in a series of 440 BC. Then, we selected 248 specimens classified as luminal (ER/PR-positive and HER2-negative) (n= 141; 57%) and TN/basal-like (ER/PR/HER2-negative +/- CK5/6 +/- EGFR) (n= 107; 43%) subtypes. Total RNA was isolated from 2-3 paraffin-embedded cylinders from preselected tumor areas and retrotranscripted to cDNA. RT-qPCR was performed by Syber Green to study the mRNA expression levels of total OPN and STAT3. Primers were tested in triplicate; RT minus and two commercial positive controls (total human and BC RNA) were included. Quantification was normalized to β-actin gene (Spearman rank correlation coefficient: r=0.82; p<0.05). Relative mRNA expression levels were carried out using the ΔΔCT method. We correlated statistically the molecular results and stratified by immunophenotypes (Chi-square and Fisher’s exact tests). Results: OPN and STAT3 mRNA overexpression (>2 fold change) was detected in 58% and 68% BC, respectively. Co-expression was seen in 40% cases with a positive predictive value (PPV) of 70% (p=0.2). However, we found no differences after stratification of the results by immunophenotypes: 33% in luminal and 46% in TN/basal-like (p=0.22). Conclusions: In our series, co-expression of OPN and STAT3 was detected in a subset of BC, supporting the regulatory role of OPN. Moreover, the fact that there was no difference among luminal and TN/basal-like phenotypes suggest that OPN control of the Jak/STAT pathway is independent of the tumor hormone receptor status. Supported by grants FCVI-HGUA/2008-PC and ACOMP/2009/195.