Cyclooxygenase-2 (COX2) and p53 protein expression are interdependent in breast cancer but not associated with clinico-pathological surrogate subtypes, tumor aggressiveness and patient survival.

Abstract

In the last decade, different molecular subtypes of breast cancer have been proposed. Although displaying appreciable association with disease prognosis and the prognostic value of cytotoxic and endocrine therapeutic modalities, the subtypes seem to fail at completely explaining disease behavior and response to treatment. Molecules such as those of the cyclocooxigenase (COX) family, currently composed of three entities (COX 1, 2 and 3) have been shown to be associated with breast carcinogenesis, and the analysis of p53 expression in breast tumors may also offer some additional prognostic clues. Our study is aimed at assessing COX2 and p53 expression in these clinico-pathological surrogate subtypes, and to evaluate whether the expression of these molecules can help further explain the variability in prognosis still found within the clinico-pathological subtypes groups of breast cancer.

Methods

A total of 183 breast cancer samples were obtained from women treated at the Womeńs Hospital of Campinas State University, Campinas, Brazil, between June 2008 and January 2011. Immunohistochemistry was performed to detect the expression of ER, PR, ki67, COX2, and p53 and the HER2 status of the 183 specimens was assessed using FISH. Two COX2 staining thresholds were used to define COX2 positivity: low threshold (LT): moderate and intense staining were considered positive; high-threshold (HT): only intense staining was considered positive.

Results

There was no trend in COX2 overexpression from Luminal A-like to Triple-negative subtypes. By contrast, p53 was expressed in roughly 67% of the Luminal A-like tumors, 50% of the Luminal B-like HER2 positive tumors, 60.9% of the Luminal B-like HER2 negative, approximately 82% of the HER2 positive (non-luminal) and 87% of the Triple-negative tumors (p for trends = 0.06). There was a significantly higher proportion of COX2 positive (LT) tumors (66.9%) when p53 was also positive compared to when the tumor was negative for p53 (in which case only18.0% of the tumors were positive for COX2; p < 0.001). Neither marker was found to be associated with patients‘ survival. Conclusions: There seems to be a positive association between the expressions of COX2 and p53. Otherwise, neither the expression of COX nor that of p53 was associated with clinico-pathological subtypes, tumor features and prognosis. It seems to be too early to elect the detection of COX2 using IHC as prognostic or predictive tool, but incipient evidence points toward a possible role for the marker.

Introduction

In the last decade, different molecular subtypes of breast cancer have been proposed, essentially following the data observed by Perou et al. (Perou et al., 2000, Perou, 2011, Sorlie et al., 2001, Sorlie et al., 2006). Recently these molecular subtypes were redefined as surrogate clinico-pathological subtypes at the St Gallen International Expert Consensus on the Primary Therapy of Early Breast Cancer 2013 (Goldhirsch et al., 2013). Although displaying appreciable association with disease prognosis and the prognostic value of cytotoxic and endocrine therapeutic modalities, the subtypes seem to fail at completely explaining disease behavior and response to treatment. The study of consolidated and novel molecules that are known to bear prognostic significance in other tumors seems to be still valid in breast pathology (Sun et al., 2014, Thorat et al., 2013, Zhou et al., 2013a, Zhou et al., 2013b). One such group of novel molecules is the cyclooxigenase (COX) family, currently composed of three entities (COX 1, 2 and 3). COX2 is the inducible isoform of the enzyme. COX2 is synthesized in the cytoplasm of cells involved in inflammatory and neoplasic processes (Thorat et al., 2013).

There is COX2 induction in in situ and invasive carcinomas, in the tumor and surrounding tissues (Fornetti et al., 2014, Glover et al., 2011, Perez et al., 2015, Serra et al., 2012). Studies demonstrated an increased expression of COX2 in Triple-negative and HER2 positive (non-luminal) tumors (Dhakal et al., 2012, Herrera et al., 2012, Perez et al., 2015, Sun et al., 2014, Thorat et al., 2013, Zhou et al., 2013a). The enzyme has also been linked to factors associated with worse prognosis such as positive axillary nodes, bone metastases, and chemotherapy resistance (Chikman et al., 2014, Dhakal et al., 2012, Herrera et al., 2012, Karavitis et al., 2012, Kim et al., 2012, Markkula et al., 2014, Thorat et al., 2013, Zhou et al., 2013a, Zhou et al., 2013b).

The analysis of p53 expression in breast tumors may also offer some additional prognostic clues. Non-functional forms of the protein can be detected by immunohistochemistry (IHC) when its encoding gene (TP53) is defective (mutated) (de Roos et al., 2007). p53 expression in breast tumors is associated with high-grade, rapidly proliferating, Triple-negative disease, and is relatively common in tumors that occur in young women (Biesaga et al., 2012, Morrison et al., 2012, Perou, 2011, Sekar et al., 2014). COX2 and p53 expression may be linked, since there is a strong relationship between TP53 mutation and inflammation (Cho et al., 2006, Serra et al., 2012). However, their relationship with the corresponding subtypes ranked by IHC as proposed in the 13th St Gallen International Breast Cancer Expert Panel Conference, 2013, and the repercussions for the treatment and prognosis according to these subtypes are not yet known.

Although scattered, there is substantial evidence suggesting a complimentary role for COX2 and p53 in evaluation of breast tumor prognosis. These molecules may add clinical information to the now standard clinico-pathological surrogate molecular classification of breast tumors. Thus, our study is aimed at assessing COX2 and p53 expression in these surrogate subtypes. In addition, we evaluated whether the expression of these molecules can help further explain the prognosis variability still found within the surrogate molecular groups of breast cancer.