Repurposing the liquid-based Pap test for the detection of ovarian cancer protein biomarkers

BACKGROUND: Earlier detection is strongly associated with increased survival for women with ovarian cancer. Unfortunately, current screening strategies, employing serial serum or ultrasound assessments, lack adequate sensitivity and specificity for use in the low-prevalence general population. In contrast, screening for cervical cancer by Pap tests has been routinely performed for over 50 years. Since ovarian cancer cells have been observed in Pap tests, ovarian cancer protein biomarkers may also be present; yet Pap samples have not been rigorously examined for diagnostic proteins. Assessment of cervical effluent, as can be collected in a Pap test, has the potential to differentiate ovarian cancer cases from healthy controls, and thereby demonstrate that intra-abdominal pathology may be detected using this commonly acquired specimen. We hypothesize that proteins shed by ovarian cancer cells can be detected in the SurePath™ liquid-based Pap test fixative using mass spectrometry (MS)-based proteomics, making it possible to distinguish women with ovarian cancer from healthy women. METHODS: Candidate ovarian cancer biomarkers were successfully identified in liquid-based Pap test samples from 20 cases of high grade serous ovarian cancer, 10 benign ovarian conditions, and 10 healthy control samples, by performing Tandem Mass Tag™ isobaric labeling, 2D liquid chromatography-MS/MS, and bioinformatics integration. Selected reaction monitoring (SRM) MS-based targeted proteomics was then performed using a panel of candidate biomarkers to quantify their abundance in an expanded patient cohort of 90 liquid-based Pap tests. RESULTS: A multi-protein classifier was developed using the SRM-MS data comprised of 6 proteins and achieving an AUC of 0.880 (95% CI: 0.738-0.989); sensitivity at 90% specificity was 0.800. CONCLUSION: This pilot study provides evidence that the cervical effluent collected in SurePath™ fixative from Pap tests has the potential to be used as a biospecimen for the detection of ovarian cancer proteins. Our long-term goal is to develop a noninvasive screening test that can be incorporated into a routine Pap test or a self-administered home test, so that women can be screened simultaneously for cervical and ovarian cancer.