Conventional and Proteomic Technologies for the Detection of Early Stage Malignancies: Markers for Ovarian Cancer

The relationship between tumor size and stage in early versus advanced ovarian cancer

BACKGROUND

Ovarian cancer has a different prognosis between early (I and II) and advanced stage (III and IV). The mechanism of disease progression is unknown, but patients with advanced disease may have a higher propensity for seeding of the abdominal cavity early in the disease process than those with early stage. Theoretically if this is so, then patients with advanced stage should have smaller sized tumors than patients with early stage.

METHODS

This was a retrospective chart review of patients in the tumor registry in 2003-2006. Patients had epithelial ovarian cancer, other cell types were excluded. Only cases with documentation of surgical and pathologic staging and measured dimensions on pathologic specimen were included. Patient stage and all available dimensions measured on diseased ovaries were recorded. The dimensions for each patient were averaged into a single dimension for that patient, and then these measurements were totaled and averaged.

RESULTS

There were 110 patients analyzed: 85 with advanced disease, 25 with early stage. The average measurement was 4.8 cm in advanced disease, and was 10.7 cm in early stage disease. This difference was statistically significant (p<0.001).

CONCLUSIONS

Overall, patients with early stage ovarian cancer have diseased ovaries that are more than twice as large as those found in advanced disease. This finding supports the fact that early versus advanced ovarian cancer are 2 separate disease processes. Early stage grows locally and does not disseminate, and advanced stage disseminates while the tumor is still relatively small. Theoretically there may be a factor that separates these 2 into different diseases, where advanced disease patients have a substance produced by their tumor that allows for early dissemination, and early stage lacks this substance and only grows locally. Basic science research comparing the tissue microarrays of early versus advanced stage disease may be able to identify this difference. If the difference is found, perhaps therapy can be targeted against this difference, and screening tests for advanced ovarian cancer can be improved.

Identification of candidate biomarkers in ovarian cancer serum by depletion of highly abundant proteins and differential in-gel electrophoresis

Ovarian cancer is the fifth leading cause of cancer death for women in the US, yet survival rates are over 90% when it is diagnosed at an early stage, highlighting the need for biomarkers for early detection. To enhance the discovery of tumor-specific proteins that could represent novel serum biomarkers for ovarian cancer, we depleted serum of highly abundant proteins which can mask the detection of proteins present in serum at low concentrations. Three commercial immunoaffinity columns were used in parallel to deplete the highly abundant proteins in serum from 60 patients with serous ovarian carcinoma and 60 non-cancer controls. Medium and low abundance serum proteins from each serum pool were then evaluated by the quantitative proteomic technique of differential in-gel electrophoresis. The number of protein spots that were elevated in ovarian cancer sera by at least twofold ranged from 36 to 248, depending upon the depletion and separation methods. From the 33 spots picked for MS analysis, nine different proteins were identified, including the novel candidate ovarian cancer biomarkers leucine-rich alpha2 glycoprotein-1 and ficolin 3. Western blotting validated the relative increases in serum protein levels for three of the proteins identified, demonstrating the utility of this approach for the identification of novel serum biomarkers for ovarian cancer.

Proteomic identification of overexpressed PRDX 1 and its clinical implications in ovarian carcinoma

Ovarian carcinoma is the most lethal gynecological malignancy in worldwide. The discovery of reliable marker for early detection of ovarian carcinoma is critical for increasing patient's survival because high mortality rate is associated with late diagnosis of this tumor. In the present study, we performed comparative analysis of whole proteomes between serous borderline tumor and serous carcinoma to identify a useful biomarker for the early diagnosis and progression of ovarian carcinoma. Nine proteins were significantly overexpressed in ovarian serous carcinomas compared to borderline tumors. After validation with Western blotting and immunohistochemical analysis, prdx 1 was found to be the strongest overexpressed protein in malignant ovarian tumors among the selected proteins. In addition, the high level of prdx 1 expression (>50% positive cancer cells) was significantly correlated with poor overall survival in ovarian serous carcinomas. On a multivariate cox analysis, the relative risk of death was 8.74 in patients with serous carcinomas showing >50% of prdx 1-positive cancer cells. Our results suggest that prdx 1 may be a useful diagnostic and prognostic biomarker in ovarian carcinoma, especially serous carcinoma.

Biomarker discovery in ovarian cancer

Ovarian cancer is a leading cause of gynecologic cancer death among women. Tumors diagnosed early (in stage I) have a cure rate approaching 90%. However, because specific symptoms and screening tools are lacking, most ovarian cancers are very advanced when finally diagnosed. CA125 expression and pelvic ultrasonography are of limited efficacy in screening, and the search for new, complementary ovarian cancer biomarkers continues. New technology and research techniques have allowed the identification of over 100 possible tumor markers, many of which are still being evaluated for clinical relevance and several of which have entered clinical trials. Here, we review the methods of biomarker discovery, address the significance and functions of newly identified ovarian cancer tumor markers, and provide further insight into the future of ovarian cancer biomarkers.

Mass spectrometry-based biomarker discovery: toward a global proteome index of individuality

Biomarker discovery and proteomics have become synonymous with mass spectrometry in recent years. Although this conflation is an injustice to the many essential biomolecular techniques widely used in biomarker-discovery platforms, it underscores the power and potential of contemporary mass spectrometry. Numerous novel and powerful technologies have been developed around mass spectrometry, proteomics, and biomarker discovery over the past 20 years to globally study complex proteomes (e.g., plasma). However, very few large-scale longitudinal studies have been carried out using these platforms to establish the analytical variability relative to true biological variability. The purpose of this review is not to cover exhaustively the applications of mass spectrometry to biomarker discovery, but rather to discuss the analytical methods and strategies that have been developed for mass spectrometry-based biomarker-discovery platforms and to place them in the context of the many challenges and opportunities yet to be addressed.

Early detection of ovarian cancer

Ovarian cancer is associated with an overall mortality of 75%, but can be cured in up to 90% of cases if diagnosed while still limited to the ovaries. Given the low prevalence of ovarian cancer in the general population, an effective screening strategy must not only have a high sensitivity for early-stage disease (>75%), but must also have a very high specificity (99.6%) to prompt no more than ten operations for each case of ovarian cancer diagnosed (positive predictive value [PPV] of 10%). Attempts to develop an effective screening strategy for ovarian cancer have utilized ultrasonography and serum tumor markers. Transvaginal sonography (TVS) and the serum marker CA125 have received the most attention to date. Used individually on a single occasion, neither of these approaches provides an adequate PPV and the cost of annual TVS is significant. Recent clinical trials have focused on serial monitoring of CA125 and the sequential use of a rising CA125 to prompt TVS in a limited number of women screened. Sequential monitoring of CA125 has significantly improved specificity of the assay in women over 50 years of age. The limited sensitivity of CA125 has, however, prompted a search for multiple serum markers that, in combination, would detect more than 90% of early-stage disease. Recent developments in genomic and proteomic research have identified a number of candidate biomarkers. Platforms have been developed that can assay more than 50 analytes in a few hundred microliters of serum. Panels of biomarkers have been discovered with high sensitivity and specificity for early-stage disease, but these require prospective validation. Several biomarkers have also been detected in urine, raising the possibility of a less expensive, more convenient screening test. Imaging techniques have been improved and mathematical methods developed that, in aggregate, promise to provide an effective screening strategy for ovarian cancer. In this review, we will assess the current status and describe future directions in ovarian cancer screening.