Epithelial cell adhesion molecule (EpCAM) is a transmembraneous glycoprotein expressed on epithelial cells. Normally it is expressed in the intercellular space connecting epithelial cells, but also on the surface of various epithelial tumor cells [1]. In tumors, EpCAM is usually not limited to the intercellular space, but expressed in a chaotic pattern over the entire surface of the tumor cell [2]. While EpCAM is one of the oldest cancer antigens, discovered as early as in 1979, it has only recently been used as a binding agent for targeted therapy in the oncologic treatment setting [3]. Efforts by different study groups have since then resulted in the development and even European Medicines Agency-approval of EpCAM-specific antibodies such as catumaxomab for treatment [4,5]. Furthermore, EpCAM might not only be used as a target for treatment but also as specific biomarker for histopathology evaluation as well as for prognosis [6,7].

While EpCAM can be found on nearly all epithelial tumor cells, the level of EpCAM-expression may significantly differ between the various histological types [7]. There is a growing evidence that these different expression levels might be of significant prognostic value [8,9,10]. A clear prognostic importance of EpCAM-expression has been observed for breast cancer, carcinomas of the gall bladder and carcinoma of the kidney and esophagus [8,10,11,12].

Epithelial ovarian cancer (EOC), one of the leading causes of cancer-related mortality in women, was found to exhibit a high level of EpCAM-expression in the majority of cases. However, only few studies have been performed to identify the prognostic value of EpCAM in EOC. Since EpCAM was found to promote carcinogenesis and invasiveness, the purpose of this study was to evaluate if EpCAM expression might be a prognostic marker in EOC. Furthermore, the level of EpCAM expression in EOC and a potential impact of EpCAM expression on chemotherapy response were our secondary aims.

Tissue samples of EOC-patients were collected during primary cytoreductive surgery after informed consent according to standard operation procedures for the Tumor Bank Ovarian Cancer project. Out of this tumor bank 74 patients were randomly selected for this analysis within a 15 year period (1994 to 2009). Twenty normal ovaries gained from other gynecological surgeries due to benign reasons and colon cancer specimens with known EpCAM overexpression were used as controls. Ethical approval was obtained by the Ethical Committee of the Charité University Medicine Berlin. All patients were chemotherapy naive at the time of the tissue collection.

Immediately after collection, the tissue was embedded in paraffin blocks and later examined by two experts of the ovarian cancer team at the Pathology Department Charité Campus Mitte. Clinical-surgical and follow-up data were collected from the validated documentation system (Intraoperative-Mapping-of-Ovarian-Cancer [IMO]), specifically developed for ovarian neoplasms with a particular focus on the description of the tumor pattern, maximal tumor burden, postoperative tumor residuals (0, <0.5, <1, <2, and >2 cm) and the amount of intraoperative ascites (none, </>500 mL). IMO represents a detailed surgical and histopathological documentation system developed to obtain a better and more objective description of the ovarian tumor spread within the abdominal cavity and to define more precisely the histopathological features of the malignancy [13]. Within the Tumor Bank Ovarian Cancer project (http://www.toc-network.de), tumor tissue, ascites, serum, and blood were collected from each EOC-patient.

All patients underwent a primary maximum tumor debulking with maximal surgical effort aiming at optimal tumor residuals, including en bloc resection techniques; most received pelvic and paraaortic lymph node dissection, peritonectomy, and upper abdominal procedures. Tumor residuals were documented after each surgery.

Seventy-four patients with primary EOC were included in the study. Median age at diagnosis was 56 years (range, 31 to 86 years). The majority of the patients (81.1%) presented with an advanced-stage International Federation of Gynecology and Obstetrics (FIGO) III/IV disease; 48.6% had positive lymph nodes; and 12.2% distant metastases. Distant metastases were found as pleural carcinosis (three patients), in the lungs (one patient), liver parenchyma (three patients), as well as axillary and inguinal lymph nodes (two patients). Detailed histopathological characteristics are presented in Table 1. During a median follow-up time of 39.7 months (range, 2.1 to 173 months) 46 of the evaluated patients (62.2%) had a relapse, and 44 patients (59.5%) have died. A complete macroscopic tumor clearance could be achieved in 52 patients (70.3%). In 11 patients (14.9%) tumor residuals were ≤1 cm and in 10 patients (13.5%) >1 cm. The majority of the patients (87.8%) received adjuvant chemotherapy. A combination of carboplatinum and paclitaxel was administered to 70.3% of the patients. The 4.1% of the patients received single-agent carboplatinum while 1.4% received single-agent paclitaxel. The 12.3% of the patients were treated with other platinum-based regimens.

In the present analysis we could identify for the first time a significant association of EpCAM overexpression with a more favorable overall survival and higher response to platinum-based chemotherapy in EOC patients. Furthermore, we could show that serous and endometrioid tumors appeared to present a significantly higher rate of EpCAM overexpressing cells as compared to mucinous tumors.

The role and the clinical implication of EpCAM in carcinogenesis remain unclear. On the one hand, there is data suggesting a positive role of EpCAM in carcinogenesis in translational as well as in clinical research. In vitro analyses might explain the beneficial properties of EpCAM by its function as cell-cell-adhesion molecule due to anticipation of tumor cell distribution [6]. Clinical studies also reported a distinct and significant positive impact of EpCAM overexpression on overall survival for renal cell, gastric, and esophageal carcinoma [8,12,15]. Patients in our collective with EpCAM overexpression had an overall survival of 49.4 months while patients with EpCAM expression ≤50% survived only 14.2 months respectively. The translational and clinical findings mentioned above could be seen as support of this data.

On the other hand, the role of EpCAM is discussed controversially as there are also reports that suggest that EpCAM-related mechanisms can promote tumor growth. Munz et al. [16] reported that EpCAM can upregulate c-myc and induce cell proliferation. Moreover, in vitro data also propose a role of EpCAM in immunosuppression and tumor cell proliferation [17,18]. Clinical studies that report EpCAM overexpression as a negative prognostic marker in breast cancer and carcinoma of the gallbladder, support these in vitro findings [9,10,11]. The fact, that EpCAM was reported as a positive prognostic marker in one tumor entity, while being linked to a negative prognosis in another, might suggest that the role of EpCAM in carcinogenesis is closely tied to the tumor biology of the different entities.

Only few data exist on EpCAM expression in ovarian cancer. To our knowledge, only two studies have analysed the prognostic significance of EpCAM overexpression in EOC [19,20]. Spizzo et al. [19] found a significant correlation of EpCAM overexpression with a worse survival in patients with EOC after primary cytoreduction, while Heinzelmann-Schwarz et al. [20] could not identify a significant impact of overexpression on survival. These findings are contrary to our results. A possible explanation could be heterogeneity clinical and histopathological characteristics of the patients. A comparison between Spizzo's collective of 199 patients and ours, showed a difference in terms of tumor stage (68% and 81.1% with FIGO stages III/IV in the collective of Spizzo compared to ours respectively) and grading (45.7% grade 3 in the study by Spizzo et al. [19] compared to 55.4% in our study), indicating that our collective was composed of more patients with advanced stages and unfavourable prognosis. Also our collective contained more patients with serous histology (40.7% and 55.4% with serous histology in the Spizzo's study and ours, respectively). In Spizzo's study it was not looked at tumor residuals and chemotherapy response. Furthermore, we also found a higher frequency of EpCAM overexpression in our collective than in the study by Spizzo et al. [19] (87.8 % vs. 68.8 %). Despite these diverse characteristics of the patient collectives, overall survival was found to be 46 months in both Spizzo's analysis and our analysis [19].

In our study, EpCAM overexpression did significantly impact overall survival in both Kaplan-Meier and Cox regression analyses. Regarding PFS, indeed, there was a significant impact of EpCAM overexpression in Cox regression analysis. This might explain the effect of overexpression on response to platinum based chemotherapy, which is, linked to PFS. Since histology had a strong influence on PFS, univariate survival analysis with the Kaplan-Meier method was not able to demonstrate a significant association of EpCAM overexpression with a longer PFS. The multivariate Cox regression model, however, that included histology in the analysis was therefore capable to show a significant impact of EpCAM overexpression on PFS despite the relatively small collective.

Another interesting finding of our analysis was the fact that mucinous histology was linked to better overall survival. This result was surprising since the mucinous subtype is mostly described to have a negative impact on prognosis. The trend for a better survival of mucinous tumors could be explained by the tumor characteristics of our mucinous tumors. As described in the results section, these tumors have a less-advanced tumor stage, a rarer lymph node involvement and a lower rate of G3 tumors. These differences are coincidental and can be drawn back to selection bias in our randomly selected sample. Based on the limited number of patients, our results have to be interpreted with caution. Nevertheless, the role of EpCAM expression in mucinous ovarian cancers is unclear and is warranted to be examined.

One of the major limitation of this study is the restricted amount of patients (n=74), making this study an exploratory analysis. The low rate of tumors without EpCAM overexpression in our collective (n=9) exposes our analyses to the risk of selection bias since the tumor samples, that were evaluated, were randomly chosen. To overcome this limitation and to minimize selection bias, a larger trial is warranted after this initial exploratory analysis.

In the light of new evolving targeted therapies such as catumaxomab and adecatumumab that use EpCAM as the main binding structure, it is necessary to further understand the role of EpCAM in ovarian cancer [4,21]. The high rate of expression noted in our analysis supports the rationale for anti-EpCAM treatment in this tumor entity.

In conclusion, our results indicate that EpCAM overexpression might be a prognostic marker in EOC, as well as a predictive factor for response to platinum-based chemotherapy.