Background

Epithelial ovarian carcinoma is a significant cause of cancer mortality in women worldwide and in the United States. Epithelial ovarian cancer comprises several histological subtypes, each with distinct clinical and molecular characteristics. The natural history of this heterogeneous disease, including the cell types of origin, is poorly understood. This study applied recently developed methods for high-throughput DNA methylation profiling to characterize ovarian cancer cell lines and tumors, including representatives of three major histologies.

Methodology/Principal Findings

We obtained DNA methylation profiles of 1,505 CpG sites (808 genes) in 27 primary epithelial ovarian tumors and 15 ovarian cancer cell lines. We found that the DNA methylation profiles of ovarian cancer cell lines were markedly different from those of primary ovarian tumors. Aggregate DNA methylation levels of the assayed CpG sites tended to be higher in ovarian cancer cell lines relative to ovarian tumors. Within the primary tumors, those of the same histological type were more alike in their methylation profiles than those of different subtypes. Supervised analyses identified 90 CpG sites (68 genes) that exhibited ‘subtype-specific’ DNA methylation patterns (FDR<1%) among the tumors. In ovarian cancer cell lines, we estimated that for at least 27% of analyzed autosomal CpG sites, increases in methylation were accompanied by decreases in transcription of the associated gene.

Significance

The significant difference in DNA methylation profiles between ovarian cancer cell lines and tumors underscores the need to be cautious in using cell lines as tumor models for molecular studies of ovarian cancer and other cancers. Similarly, the distinct methylation profiles of the different histological types of ovarian tumors reinforces the need to treat the different histologies of ovarian cancer as different diseases, both clinically and in biomarker studies. These data provide a useful resource for future studies, including those of potential tumor progenitor cells, which may help illuminate the etiology and natural history of these cancers.

Background

CA125, human epididymis protein 4 (HE4), mesothelin, B7-H4, decoy receptor 3 (DcR3), and spondin-2 have been identified as potential ovarian cancer biomarkers. Except for CA125, their behavior in the prediagnostic period has not been evaluated.

Methods

Immunoassays were used to determine concentrations of CA125, HE4, mesothelin, B7-H4, DcR3, and spondin-2 proteins in prediagnostic serum specimens (1–11 samples per participant) that were contributed 0–18 years before ovarian cancer diagnosis from 34 patients with ovarian cancer (15 with advanced-stage serous carcinoma) and during a comparable time interval before the reference date from 70 matched control subjects who were participating in the Carotene and Retinol Efficacy Trial. Lowess curves were fit to biomarker levels in cancer patients and control subjects separately to summarize mean levels over time. Receiver operating characteristic curves were plotted, and area-under-the curve (AUC) statistics were computed to summarize the discrimination ability of these biomarkers by time before diagnosis.

Results

Smoothed mean concentrations of CA125, HE4, and mesothelin (but not of B7-H4, DcR3, and spondin-2) began to increase (visually) in cancer patients relative to control subjects approximately 3 years before diagnosis but reached detectable elevations only within the final year before diagnosis. In descriptive receiver operating characteristic analyses, the discriminatory power of these biomarkers was limited (AUC statistics range = 0.56–0.75) but showed increasing accuracy with time approaching diagnosis (eg, AUC statistics for CA125 were 0.57, 0.68, and 0.74 for ≥4, 2–4, and <2 years before diagnosis, respectively).

Conclusion

Serum concentrations of CA125, HE4, and mesothelin may provide evidence of ovarian cancer 3 years before clinical diagnosis, but the likely lead time associated with these markers appears to be less than 1 year.

Objectives

To define patterns of aberrant DNA methylation, p53 mutation and Her-2/neu overexpression in tissues from benign (N=29), malignant (N=100), and border line malignant ovaries (N=10), as compared to normal (N=68) ovarian tissues. Further, to explore the relationship between the presence of genetic and epigenetic abnormalities in ovarian cancers, and assess the association between epigenetic changes and clinical stage of malignancy at presentation and response to therapy.

Methods

The methylation status of 23 genes that were previously reported associated with various epithelial malignancies was assessed in normal and abnormal ovarian tissues by methylation specific PCR. The presence of p53 mutation (N=82 cases) and Her-2/neu overexpression (N=51 cases) were assessed by DNA sequencing and immunohistochemistry, respectively.

Results

Methylation of four genes (MINT31, HIC1, RASSF1, and CABIN1) was significantly associated with ovarian cancer but not other ovarian pathology. Her-2/neu overexpression was associated with aberrant methylation of three genes (MINT31, RASSF1, and CDH13), although aberrant methylation was not associated with p53 mutations. Methylation of RASSF1 and HIC1 was more frequent in early compared to late stage ovarian cancer, while methylation of CABIN1 and RASSF1 was associated with response to chemotherapy.

Conclusion

DNA methylation of tumor suppressor genes is a frequent event in ovarian cancer, and in some cases is associated with Her-2/neu overexpression. Methylation of CABIN1 and RASSF1 may have the utility to predict response to therapy.

Objective

To evaluate if serum levels of candidate ovarian cancer biomarkers vary with individual characteristics of healthy women who are likely candidates for an ovarian cancer screening program.

Methods

We analyzed serum CA125, mesothelin and HE4 levels in a sample of 155 healthy post-menopausal women at increased risk for developing ovarian cancer based on personal and family cancer history. Information on reproductive, family and medical histories, lifestyle factors and anthropometry was collected by self-report. Twenty-two factors were examined using univariate and multiple linear regression models for the three biomarker levels.

Results

In the multivariate models, CA125 levels were significantly higher in women who had used talcum powder (P=0.02) and were lower in women who were parous (P=0.05). Mesothelin levels were significantly higher in older women (P=0.01) and lower in heavier women (P=0.03). HE4 levels were higher in older women (P=0.001) and in women who began menstruating at an older age (P=0.03).

Conclusions

CA125, mesothelin and HE4 levels in healthy, post-menopausal women at increased risk for ovarian cancer are significantly associated with a few ovarian cancer risk factors. Since the effects of these personal characteristics on these serum markers are not large, their incorporation in screening algorithms may be unnecessary. This is true especially if a longitudinal algorithm is used because the marker level at the previous screen reflects personal characteristics such as age, BMI, and age of menarche. Understanding the influence of personal factors on levels of novel early detection markers in healthy, unaffected women may have clinical utility in interpreting biomarker levels.

Purpose

Efforts to validate ovarian cancer early detection biomarkers with immunoassays are challenged by limited specimen volumes available. We sought to develop a specimen-efficient assay to measure CA125 in serum, assess its reproducibility, validity and performance, and test its potential for multiplexing and combining with HE4, a promising novel ovarian cancer marker.

Experimental Design

Four pairs of commercially available anti-CA125 antibodies and one pair of anti-HE4 antibodies were evaluated for accuracy in measuring known concentrations of antigen on a bead-based platform. Two best pairs were further assessed for reproducibility, validity, and ability to discriminate between blinded serum samples obtained from ovarian cancer cases (n=66) and women without ovarian cancer (n=125).

Results

Suitability for use in a bead-based assay varied across CA125 antibody pairs. Two CA125 bead-based assays were highly reproducible (overall correlations between replicates ≥0.95; CV’s below 0.2) and strongly correlated with the research standard CA125II RIA (correlations ≥0.9). Their ability to distinguish ovarian cancer cases from non-cases based on ROC analyses (AUCs of 0.85 and 0.84) was close to that of the CA125II RIA (AUC of 0.87). The HE4 bead-based assay showed lower reproducibility but yielded an AUC of 0.89 in ROC analysis. Multiplexing was not possible but a composite marker including CA125 and HE4 achieved an AUC of 0.91.

Conclusion

Optimization procedures yielded two bead-based assays for CA125 that perform comparably to the standard CA125II RIA, can be combined with an HE4 bead-based assay to improve diagnostic performance, and require only 15μl of sample each.

Background

MicroRNAs (miRNAs) are small regulatory RNAs that are implicated in cancer pathogenesis and have recently shown promise as blood-based biomarkers for cancer detection. Epithelial ovarian cancer is a deadly disease for which improved outcomes could be achieved by successful early detection and enhanced understanding of molecular pathogenesis that leads to improved therapies. A critical step toward these goals is to establish a comprehensive view of miRNAs expressed in epithelial ovarian cancer tissues as well as in normal ovarian surface epithelial cells.

Methodology

We used massively parallel pyrosequencing (i.e., “454 sequencing”) to discover and characterize novel and known miRNAs expressed in primary cultures of normal human ovarian surface epithelium (HOSE) and in tissue from three of the most common histotypes of ovarian cancer. Deep sequencing of small RNA cDNA libraries derived from normal HOSE and ovarian cancer samples yielded a total of 738,710 high-quality sequence reads, generating comprehensive digital profiles of miRNA expression. Expression profiles for 498 previously annotated miRNAs were delineated and we discovered six novel miRNAs and 39 candidate miRNAs. A set of 124 miRNAs was differentially expressed in normal versus cancer samples and 38 miRNAs were differentially expressed across histologic subtypes of ovarian cancer. Taqman qRT-PCR performed on a subset of miRNAs confirmed results of the sequencing-based study.

Conclusions

This report expands the body of miRNAs known to be expressed in epithelial ovarian cancer and provides a useful resource for future studies of the role of miRNAs in the pathogenesis and early detection of ovarian cancer.

Background

Epithelial ovarian cancer is a significant cause of mortality both in the United States and worldwide, due largely to the high proportion of cases that present at a late stage, when survival is extremely poor. Early detection of epithelial ovarian cancer, and of the serous subtype in particular, is a promising strategy for saving lives. The low prevalence of ovarian cancer makes the development of an adequately sensitive and specific test based on blood markers very challenging. We evaluated the performance of a set of candidate blood markers and combinations of these markers in detecting serous ovarian cancer.

Methods and Findings

We selected 14 candidate blood markers of serous ovarian cancer for which assays were available to measure their levels in serum or plasma, based on our analysis of global gene expression data and on literature searches. We evaluated the performance of these candidate markers individually and in combination by measuring them in overlapping sets of serum (or plasma) samples from women with clinically detectable ovarian cancer and women without ovarian cancer. Based on sensitivity at high specificity, we determined that 4 of the 14 candidate markers-MUC16, WFDC2, MSLN and MMP7-warrant further evaluation in precious serum specimens collected months to years prior to clinical diagnosis to assess their utility in early detection. We also reported differences in the performance of these candidate blood markers across histological types of epithelial ovarian cancer.

Conclusions

By systematically analyzing the performance of candidate blood markers of ovarian cancer in distinguishing women with clinically apparent ovarian cancer from women without ovarian cancer, we identified a set of serum markers with adequate performance to warrant testing for their ability to identify ovarian cancer months to years prior to clinical diagnosis. We argued for the importance of sensitivity at high specificity and of magnitude of difference in marker levels between cases and controls as performance metrics and demonstrated the importance of stratifying analyses by histological type of ovarian cancer. Also, we discussed the limitations of studies (like this one) that use samples obtained from symptomatic women to assess potential utility in detection of disease months to years prior to clinical detection.

Background

Elucidation of the repertoire of secreted and cell surface proteins of tumor cells is relevant to molecular diagnostics, tumor imaging and targeted therapies. We have characterized the cell surface proteome and the proteins released into the extra-cellular milieu of three ovarian cancer cell lines, CaOV3, OVCAR3 and ES2 and of ovarian tumor cells enriched from ascites fluid.

Methodology and Findings

To differentiate proteins released into the media from protein constituents of media utilized for culture, cells were grown in the presence of [13C]-labeled lysine. A biotinylation-based approach was used to capture cell surface associated proteins. Our general experimental strategy consisted of fractionation of proteins from individual compartments followed by proteolytic digestion and LC-MS/MS analysis. In total, some 6,400 proteins were identified with high confidence across all specimens and fractions.

Conclusions and Significance

Protein profiles of the cell lines had substantial similarity to the profiles of human ovarian cancer cells from ascites fluid and included protein markers known to be associated with ovarian cancer. Proteomic analysis indicated extensive shedding from extra-cellular domains of proteins expressed on the cell surface, and remarkably high secretion rates for some proteins (nanograms per million cells per hour). Cell surface and secreted proteins identified by in-depth proteomic profiling of ovarian cancer cells may provide new targets for diagnosis and therapy.

Under-representation of minority and female participants prompted the U.S. legislature to mandate the inclusion of women and minorities in federally funded research. Recruitment of minorities to participate in clinical trials continues to be challenging. Although Asian Americans constitute one of the major minority groups in the U.S., published literature contains sparse data concerning the participation of Asian Americans in cancer clinical trials. The authors completed qualitative, semistructured interviews with 34 participants: Chinese-American female cancer patients ages 20–85 years or their family members. Interviews were conducted in Cantonese, Mandarin, or English and were audiotaped. Chinese interviews were translated into English, and all interviews were transcribed subsequently into English. A team of five coders individually reviewed then met to discuss the English transcripts. The authors used the constant comparative technique throughout the entire coding process as part of the analysis. Among participants, 62% lacked any knowledge of clinical trials, and many expressed negative attitudes toward clinical trials. Barriers to participation included inadequate resources, language issues, and a lack of financial and social support. Facilitating factors included recommendations by a trusted oncologist or another trusted individual and information in the appropriate language. It is noteworthy that family members played an important role in the cancer experience of these participants. To promote participation, there is a need to increase knowledge of clinical trials among Chinese cancer patients. It also is necessary to examine the applicability of current patient-physician communication and interaction models. In addition, decision-making based on Asian philosophies within the context of Euro-American bio-ethics requires further study.