Abstract P6-07-09: Identification of Trophinin associated protein (TROAP) as a novel biological marker in breast cancer (BC): Co-expression of TROAP and TOPO2A predicts response of anthracycline based chemotherapy (ATC-CT)

Abstract

Abstract Introduction: Recently, TOPO2A alteration was found to be a predictor for ATC-CT and by using neural network and pathways analysis of gene expression array data, TROAP gene was revealed as a major hub in TOPO2A pathway and strongly related to genes that are involved in mitotic cell cycle regulation. In addition, we found that TROAP gene was among top 10 ranked genes out of 48,000 of transcripts, that accurately predicted worse clinical outcome, and differentiated between low and high grade based on a 10-fold external cross-validation analysis with an average classification accuracy of >99.999%. TROAP protein is essential for centrosome integrity and proper bipolar organisation of spindle assembly during mitosis and plays essential role in cell proliferation. In the current study the molecular and clinicopathological functions of TROAP expression and its effect on management of breast cancer have been investigated. Methods: The co-expression of TROAP and TOPO2A protein was evaluated by using dual immunoflurescent in BC cell lines. In addition both TROAP and TOP2A protein expressions were immunohistochemically (IHC) assessed in 40 normal breast tissues and a well characterised series of 1650 primary BC and were correlated to clinicopathological and other biomarkers. IHC staining was performed using Anti-TROAP rabbit polyclonal (HPA044102; Sigma). The association between TROAP and response to chemotherapy was investigated in 350 ER negative BC treated with adjuvant ATC-CT and 260 locally advanced BC treated with neoadjuvant ATC-CT. In addition the clinical outcome of TROAP expression was evaluated in a series of 180 ER− high risk BC patients who did not received any CT. Results: No expression of TROAP protein was observed in normal breast tissue while, 25% of BC showed TROAP protein overexpression. By using dual immunoflurescent in BC cell lines, The MCF7 cells showed strong cytoplasmic TROAP staining with no TOPO2A expression, while The T47D cells did not express TROAP but expressed TOPO2A. SKBr3, MDA468 and MDA231 cell lines showed co-expression of TROAP and TOPO2A. TROAP overexpression was significantly associated with aggressive clinico-pathological features including; high grade, high mitotic rate, absence of hormonal receptors, overexpression of HER2, TOP2A and EGFR (p < 0.001), Triple negative phenotype (p < 0.001), basal-like BC (p < 0.001), p53 mutation (p < 0.001) and inactive p16 (p < 0.001). With regard to outcome, receiving anthracycline chemotherapy had a positive impact on high risk ER− BC patients with TROAP protein over-expression as TROAP protein overexpression showed 50% less risk of recurrence compared to TROAP negative expression; p < 0.0001. Moreover, in locally advanced BC who received anthracycline-based neoadjuvant chemotherapy, 31/81 (39%) of BC with co-expression of TROAP+/TOPO2A+ achieved pCR while none of those with absence of both TROAP−/TOPO2A− (0/51) had achieved pCR (p < 0.00001). Conclusion: TROAP is an important novel gene implicated in the survival of BC cells and its protein expression is a predictor for Anthracycline CT. TROAP may provide new avenues for the discovery of new predictive marker to guide therapeutic intervention. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-07-09.