Original contributionThe combination of high cyclin E and Skp2 expression in breast cancer is associated with a poor prognosis and the basal phenotype☆,☆☆
Introduction
Gene expression analyses of multiple breast cancer cohorts have consistently demonstrated a separation of estrogen receptor (ER)–negative breast cancers into HER2 positive and basal subtypes [1], [2], [3]. The basal breast cancers are associated with a particularly poor prognosis, and, as they are both ER negative and HER2 negative, these patients do not benefit from adjuvant hormonal therapy or trastuzumab. Currently, there is uncertainty regarding the identification of the basal breast cancers—the “gold standard” definition is by gene expression profile, but proposed immunohistochemical surrogate panels include the triple-negative definition (ER negative, PR negative, and HER2 negative) and more specific panels incorporating positive markers of the basal phenotype (ER negative, HER2 negative, and either epidermal growth factor receptor [EGFR] or CK5/6 positive) [4], [5]. Further study into the molecular characteristics of basal breast cancers may lead to the discovery of potential therapeutic targets. Recent studies characterizing this subtype have found that, when studied individually, the expression of cyclin E and Skp2, and the absence of p27 (the product of the KIP1 gene) are each associated with basal breast cancers [6], [7]. In addition, these 3 proteins are linked through a common molecular pathway that regulates the cell cycle at the G1/S checkpoint. Loss of this checkpoint results in genomic instability and the development of neoplasia [8].
Cyclin E and its associated cyclin-dependent kinase, CDK2, promote cell-cycle progression. Overexpression of cyclin E was shown to have independent prognostic significance in a cohort of patients with breast cancer [9], [10]. p27 is an inhibitor of the cyclin E/CDK2 complex and as such functions as a tumor suppressor [11], [12]. In addition, some studies suggest that p27 can predict response to chemotherapy [13] and hormone therapy [14], [15]. Skp2 is a ubiquitin ligase that targets p27 for degradation [16] and also has an oncogenic role in breast cancer [7], [17]. Although cyclin E, p27, and Skp2 have not yet seen widespread use as clinical biomarkers, they have the potential to improve prognostic models and possibly predict response to adjuvant treatment. However, some follow-up studies have failed to confirm these previous findings. In this study, we use tissue microarrays (TMAs) to analyze the expression of these 3 biomarkers on a cohort of 438 breast cancer samples linked to long-term clinical outcome data. By combining these biologically linked biomarkers, we aimed to create a more specific test to isolate a clinically important breast cancer subgroup. We hypothesized that the novel combination of cyclin E positive, p27 negative, and Skp2 positive, which we will refer to as the 3-marker phenotype, would identify a particularly high-risk subgroup of breast cancer and be associated with the basal breast cancer phenotype.
Section snippets
Materials and methods
Our study population is a single institution cohort comprising 438 patients who had surgery for breast neoplasia at the Vancouver General Hospital between 1974 and 1995. Detailed clinicopathologic and outcome data were available for all patients. Because our patients were accrued from an extended period, and the treatment of breast cancer has changed significantly, we did not include treatment data in our analysis. Patients presenting with metastatic disease, patients with in situ disease only,
Results
The mean age of our patient cohort was 60 years and the median follow-up 15 years. Fifty-two percent had tumors greater than 2 cm, and 54% had grade 3 tumors. Thirty-five percent were node negative, 80% were ER positive, and 14% were HER2 positive.
For the biomarkers specific to this study, cyclin E was positive in 46% of cases, Skp2 was positive in 35%, and p27 was negative in 62% (Table 1). Representative images are presented in Fig. 1 and all primary image data are available at //www.gpecimage.ubc.ca/tma/web/viewer.php
Discussion
There have been several published studies that reported on the prognostic value of cyclin E, p27, and Skp2 as individual biomarkers in breast cancer. All 3 proteins are linked through a common biological pathway, playing a central role in cell-cycle regulation. This is the first study that has combined these markers as a 3-marker phenotype.
Cyclin E forms a complex with CDK2 and promotes G1/S cell-cycle progression. The CCNE gene is amplified in some breast cancer cell lines [27], and it is
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2017, Seminars in OncologyCitation Excerpt :Furthermore, ER+ and HER2+ cell lines also tend to have functional phosphorylated Rb, whereas basal type breast cancers are more likely to have Rb loss and are driven by alternative pro-mitogenic signals [33–35] (Table 2). Similarly, cyclin E is more commonly overexpressed in basal tumors and is associated with poor prognosis, as compared with the overexpression of cyclin D1 in luminal subtypes [34,36]. In this manner, cyclin E may be an alternate driver of Rb phosphorylation to promote S phase transition, despite inhibition of the cyclin D1-CDK4/6 complex [37].
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2017, European Journal of CancerCitation Excerpt :Central to the cell cycle are the cyclin family of proteins that regulate cellular growth and division in both normal and malignant cells. Cyclins display subtype-specific expression in breast cancer [22,23] and are generally expressed in higher levels in young women [24–26], potentially contributing to age-related differences in disease-specific survival. Despite their central role in breast cancer oncogenesis, it is currently unclear whether cyclins retain their prognostic value in young women when taking other strong prognostic indicators such as age and subtype into account.
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2016, Biochimica et Biophysica Acta - Reviews on CancerCitation Excerpt :On the other hands, overexpression of Skp2 in mice led to tumor development including lymphoma [116], prostate cancer [114], and mammary gland tumor [113]. Consistently, overexpression of Skp2 has been frequently observed in a variety of human cancers such as lymphomas [117,118], pancreatic cancer [119], breast carcinomas [120–124], prostate cancer [125,126], melanoma [127–129], and nasopharyngeal carcinoma [130,131]. Importantly, Skp2 expression is associated with histological grade and tumor size in hepatocarcinoma [132].
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2016, American Journal of PathologyCitation Excerpt :In our study, immunostaining for cytoplasmic cyclin E was strongly associated with high tumor grade. This finding was similar to those of previous studies that reported a relation between cyclin E overexpression and high histologic grade.2,3,5,8,40–44 We also found a strong association between histologic subtype and cyclin E immunostaining pattern.
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This study examines a novel combination of breast cancer immunohistochemical biomarkers on a large tissue microarray with long follow-up. We show that this combination has prognostic value and is closely associated with the basal breast cancer phenotype.
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This work was supported by a grant from the Canadian Breast Cancer Research Alliance to WDF and TON. The Genetic Pathology Evaluation Centre is supported by an unrestricted educational grant from Sanofi-Aventis.