ERCC1-expressing circulating tumor cells as a potential diagnostic tool for monitoring response to platinum-based chemotherapy and for predicting post-therapeutic outcome of ovarian cancer

Abstract

Background: We recently showed that the presence of ERCC1+CTCs is an independent predictive biomarker for platinum-resistance and poor prognosis of ovarian cancer. The goal of our current research was to determine how the auxiliary assessment of ERCC1-transcripts influences overall CTC-detection rate. We extended this investigation from an initially predictive setting to paired pre- and post-therapeutic blood analysis in order to see, whether ERCC1+CTCs dynamics mirror response to chemotherapy.

Methods: 65 Paired blood samples (10ml) of primary ovarian cancer patients at primary diagnosis and after chemotherapy were studied for CTCs with the AdnaTest Ovarian Cancer (QIAGEN Hannover GmbH). We analyzed the tumor-associated transcripts EpCAM, MUC-1 and CA-125. ERCC1-transcripts were investigated in a separate approach by singleplex RT-PCR.

Results: Auxiliary assessment of ERCC1-transcripts enhanced the overall CTC-detection rate up to 17%. ERCC1+CTCs (defined as positive for one of the AdnaTest markers plus ERCC1-positivity) were detected in 15% of patients at primary diagnosis and in 12% after chemotherapy. The presence of ERCC1+CTCs after chemotherapy correlated with platinum-resistance (P=0.01), reduced PFS (P=0.0293) and OS (P=0.0008) and their persistence indicated poor post-therapeutic outcome (PFS: P=0.005; OS: P=0.0058). Interestingly, the assessment of ERCC1-transcripts alone was sufficient for the detection of prognostic relevant ERCC1-expressing CTCs.

Conclusion: Auxiliary assessment of ERCC1-transcripts expands the phenotypic spectrum of CTC detection and defines an additional overlapping fraction of ERCC1-expressing CTCs, which are potentially selected by platinum-based chemotherapy. Specifically, we suggest that ERCC1+CTCs could additionally be useful as a surrogate for monitoring platinum-based chemotherapy and to assess the post-therapeutic outcome of ovarian cancer.

Keywords: ERCC1; circulating tumor cells; ovarian cancer; platinum-resistance; prognosis.

Figure 1. Influence of auxiliary ERCC1-transcript assessment on CTC-detection rate

A. The pie chart shows the different CTC-types and their relative proportions among the studied ovarian cancer patients before surgery (n=65). Percentages indicate the proportion of patients with exclusively-Adnatest-positivity (yellow), exclusively-ERCC1-positivity (blue), dual-positivity for Adnatest/ERCC1 (green) and CTC-negative patients (grey). B. The stacked bar chart summarizes four CTC-definition criteria, considering ERCC1 as additional transcript marker and shows, how this is translated into different overall CTC-detection rates. C+D. These illustrations depict the same type of analysis as reported above, however refer to paired blood samples analyzed after platinum-based chemotherapy (n=65). In all figures, absolute patient numbers in each subgroup are indicated.

Figure 2. Prognostic relevance of ERCC1⁺CTCs after chemotherapy

A patient was considered positive for ERCC1⁺CTCs if at least one of the AdnaTest transcript markers (EpCAM, MUC-1 or CA-125) was detected, in addition to ERCC1-positivity. The Kaplan-Meier analysis shows A. progression-free survival and B. overall survival of patients with detectable ERCC1⁺CTCs after platinum-based chemotherapy (bottom curves) in comparison to patients with non-detectable ERCC1⁺CTCs (top curves).

Figure 3. Dynamics of ERCC1⁺CTCs in the course of platinum-based chemotherapy

A patient was considered positive for ERCC1⁺CTCs if at least one of the Adnatest transcript markers (EpCAM, MUC-1 or CA-125) was detected, in addition to ERCC1-positivity. The pie chart shows a stratification of the study cohort (n=65) into different subgroups, according to the dynamics of ERCC1⁺CTCs before surgery and after chemotherapy. Besides the group of patients, who were negative for ERCC1⁺CTCs throughout (ERCC1⁺CTCs neg-neg), we observed patients, who became negative after chemotherapy (ERCC1⁺CTCs pos-neg), patients with newly acquired positivity after chemotherapy (ERCC1⁺CTCs neg-pos) or persistently positive patients (ERCC1⁺CTCs pos-pos). Percentages and absolute patient numbers are indicated.

Figure 4. Prognostic relevance of persistent ERCC1⁺CTCs

The Kaplan-Meier plots show A. progression-free survival and B. overall survival of patients with persistent positivity for ERCC1⁺CTCs in their blood (ERCC1⁺CTC pos-pos, bottom curves), in comparison to all other dynamic subgroups together (ERCC1⁺CTC pos-neg / neg-pos / neg-neg, top curves). Moreover, Kaplan-Meier plots show C. progression-free survival and D. overall survival of patients with newly acquired positivity for ERCC1⁺CTCs (ERCC1+CTC neg-pos, bottom curves), in comparison to the dynamic subgroups ERCC1⁺CTC pos-neg and ERCC1⁺CTC neg-neg, together (top curves).

Figure 5. Prognostic relevance of ERCC1-transcripts alone

This analysis refers to the prognostic relevance of ERCC1-transcripts alone, irrespectively of the Adnatest transcript markers EpCAM, MUC-1 or CA-125. The Kaplan-Meier plots show A. progression-free survival and B. overall survival of patients with ERCC1-positivity after platinum-based chemotherapy (bottom curves) in comparison to patients with non-detectable ERCC1-transcripts (top curves). Moreover, Kaplan-Meier plots show C. progression-free survival and D. overall survival of patients with persistent positivity for ERCC1-transcripts (ERCC1⁺ pos-pos, bottom curves) in comparison to all other dynamic subgroups together (ERCC1⁺ pos-neg / neg-pos / neg-neg, top curves).