Overexpression of connective tissue growth factor is associated with tumor progression and unfavorable prognosis in endometrial cancer

1. Introduction

Endometrial cancer (EC) is one of the most common malignancies affecting the female reproductive tract [1]. However, the molecular and genetic events underlying the development of these tumors remain obscure [2]. The disease most commonly presents with abnormal uterine bleeding and consequently, is often detected in early stages (FIGO stage I) [3]. However, some patients present with advanced stage disease. 35% of the endometrial cancers are diagnosed in the advanced stage of the disease, and with significantly diminished lifetime expectancy [4]. Hysterectomy with bilateral salpingo-oophorectomy is the primary treatment for patients with this localized disease. Thus, there is an urgent need for new therapeutic targets and strategies for endometrial tumorigenesis, both of which may be realized through improved understanding of the molecular mechanisms governing this disease.

Connective tissue growth factor (CTGF), also known as CCN2, belongs to the CCN (CTGF/Cysteine-rich 61/Nephroblastoma) family [5]. All CCN family members are secreted proteins associated with the extracellular matrix (ECM) which play an essential role in processes such as placentation, embryo implantation, embryogenesis, differentiation, and development. These proteins are also implicated in wound healing, fibrotic disorders, and tumorigenesis [6, 7]. Interestingly, the role of CTGF varies depending on the type of cancer. For example, CTGF is an oncogenic factor which promotes tumor progression in pancreatic, prostate, liver, and breast cancer, ovarian cancer as well as sarcomas [8, 9]. Conversely, CTGF functions as a tumor suppressor in the lung, and oral squamous cell cancers [10, 11, 12]. CTGF has been used as a prognostic marker in esophageal squamous cell carcinoma, gastric and lung cancer [10, 13]. However, the expression pattern and functional mechanisms of CTGF in EC have not been established.

In the present study, we examined the expression of CTGF in normal and malignant endometrial tissue in order to determine its involvement in malignant progression. Additionally, we evaluated whether CTGF expression is associated with clinical-pathologic parameters and prognosis in patients with EC.

2. Materials and methods

3. Results

Historically, the age of onset of EC is mostly after menopause. However, the incidence of EC in premenopausal women has increased dramatically due to earlier-onset obesity in the past ten years [15]. Even though there are effective treatment methods, survival is still based on the stage and histology of the diagnosis. Most EC patients with stage I-II will have a favorable prognosis, whereas patients with stage III or IV will have a worse likelihood of survival [16, 17, 18]. Although CA125 remains as one the most widely used biomarkers for the potential diagnosis and prognosis of EC [19, 20, 21, 22], it demonstrates several limitations, including the occurrence of false-positive diagnosis and over-treatment due to the reduced sensitivity and specificity of CA125 level testing [23, 24]. Therefore, it is of a high clinical significance to find specific valuable biomarkers which can screen high-risk women, make a preoperative stratification of patients as high-risk or low-risk categories, support personalized therapeutic approaches.

In the present study, we detected high CTGF expression in 52% of EC patients, which is significantly higher than 16% in normal endometrial tissues. The CTGF expression was predominantly observed in the cytoplasm and membrane of cancer cells. The rate of positive CTGF expression was increased significantly in poorly-differentiated EC, levels of CA125 expression ï ⁢ ¼ ⁢ ž 35 U/mL, depth of myometrial invasion ⩾ 1/2, FIGO stage III-IV. Furthermore, CTGF expression was positively associated with CA125 levels in EC patients. The elevated CA125 level was reported firstly to be an essential predictor for patients with recurrent and advanced EC [25]. Since then, many studies have confirmed that the determination of CA125 before surgery is a prognostic factor for overall survival (OS) and disease-free survival (DFS) in EC [26, 27]. The level of CA125 was significantly higher in patients with more advanced FIGO stage [26]. In the present study, a markedly increased CTGF level was observed in EC patients in FIGO III-IV when compared to FIGO I-II, and the level of CTGF was positively associated with the CA125. Therefore, the CTGF protein level potentially can function as a novel prognostic biomarker to distinguish the EC patients which has more advanced FIGO stage, besides, it has a potential role to predict the poor survival of EC patients.

Interestingly, a recent study demonstrated that CTGF expression was increased in epithelial ovarian cancer tissues, and its expression correlated with the stage of this disease. The CTGF levels in stage III-IV of ovarian cancer were significantly higher than stage I-II [28]. These are consistent with our findings and indicate that over-expression of CTGF may contribute to the progression of EC. The mechanism of CTGF in mediating the EC progression is unclear. However, CTGF had been found to accelerate tumor progression through mediating tumor-stroma interactions between hepatoma cells and hepatic stellate cells [29]. There is a positive feedback loop between CTGF and chemokine ligand 18 in hepatocellular carcinoma metastasis [30]. Thus, promoting tumor-stroma interactions might be one of the mechanisms which are mediated by CTGF to accelerate tumor progression.

Univariate and multivariate analysis revealed that high CTGF expression was a powerful independent predictor for the poor survival of EC patients. The overall 5-year survival rate of EC patients with a positive CTGF expression and a negative CTGF expression was 36.8% and 80.9%, respectively. Our results indicated that over-expression of CTGF might play a role in the aggressive behavior of EC. These are consistent with various studies which showed that CTGF is associated with a more aggressive phenotype and with tumor progression in kind of solid tumor tissues [8, 31, 32, 33, 34, 35, 36, 37, 38, 39]. Dr. Kang and colleagues found that CTGF is a critical component of the gene signature that facilitates osteolytic bone metastasis in breast cancer cells [40]. Administration of FG-3019, a humanized anti-CTGF monoclonal antibody, inhibits tumor growth and metastases in xenograft and orthotopic models of pancreatic cancer in mice [35, 41]. Therefore, CTGF up-regulation in EC may promote the tumor growth and metastases which is associated with a lower survival rate of the patients.

The mechanisms responsible for CTGF over-expression in EC patient needs further investigation to elucidate. Recent studies demonstrated that microRNAs are essential mediators in the mechanism of human cancer. MiR-143 was reported to target CTGF and exert tumor-suppressing functions in epithelial ovarian cancer [42]. In addition to MiR-143, MiR-26b was also found to govern the CTGF expression in osteosarcoma. When MiR-26b levels sharply increased, the CTGF expression was downregulated [43]. Based on these findings, we speculated that MiR-143 and MiR-26b might be a potential regulator of CTGF. However, further investigations are still needed to verify the above-mentioned underlying mechanisms.

In conclusion, our findings indicated that on clinical inspection, EC patients with increased CTGF expression have more chance to develop to the advanced stage of EC and shorter survival time. Mainly, CTGF seemed to be an independent prognostic factor that will allow the successful differentiation of high-risk population from the group of patients with stage III-IV disease. Moreover, CTGF seems to be a novel biomarker for predicting the prognosis of EC patients. Also, over-expression of CTGF in EC patients results in poor survival.