This study was performed in the context of a cooperative trial with other SPORE, EDRN and PLCO investigators that evaluated some 35 different biomarkers in proximal pre-diagnostically collected serum samples from 118 women who subsequently developed ovarian cancer. In evaluating samples obtained prior to conventional diagnosis, the addition seven biomarkers to CA125 in a combined multi-marker panel did not improve the sensitivity over that obtained with CA125 alone at 98% specificity. CA125 was originally used to monitor women known to have ovarian cancer 15,16
as changes in CA125 levels can track the progression or regression of disease during treatment with up to 90% accuracy. Persistent elevation of CA125 following surgery and chemotherapy indicates the presence of residual disease. When multiple serum samples are evaluated, rising levels of CA125 can detect recurrent ovarian cancer with an average lead time of at least 3 months. CA125 can also be elevated many months prior to cancer diagnosis.16
In the current study, using one pre-diagnostic serum sample from PLCO Trial participants, CA125 was elevated (≥35 U/mL) in 61% of cases sampled within the 12 months prior to diagnosis and in 31% of the patients sampled more than 1 year prior to diagnosis. Observation of elevated CA125 in a significant fraction of patients >12 months prior to diagnosis can be considered an encouraging outcome.
Despite the observed lead time in the pre-diagnostic samples, the positive predictive value of CA125 was only 3.7% in the PLCO Trial. While the specificity of CA1252
can approach 99% in postmenopausal women, given the very low prevalence of ovarian cancer (1 in 2,500 among postmenopausal women), 99.6% specificity is required to achieve a positive predictive value of 10%, meaning that there are less than 10 surgeries for each diagnosed ovarian cancer case. Specificity of CA125 was improved by combining biomarker results with TVS. In the PLCO Trial, if CA125 was elevated and a TVS was abnormal, the positive predictive value increased to 23.5%, although 60% of the invasive cancers would not have been detected.2
Specificity of CA125 can also be increased by studying changes in levels over time. An algorithm using age and change point analysis to determine whether levels have increased beyond the subject’s own baseline when compared to annual determinations17
is being evaluated in a study of 202,638 British woman (UKCTOCS).18
TVS result combined with rising CA125 levels with time produced a sensitivity of 89.5%, a specificity of 99.8% and a positive predictive value of 35%. Overall, 48% of the prevalent cancers were detected in stage I or II, twice the fraction expected using conventional diagnostic methods. In the U.S., a similar screening trial of 3,252 postmenopausal women followed annually with CA125 using the same algorithm coordinated by the Ovarian SPORE at MDACC.19
Less than 1% of patients were referred for TVS each year and less than 3% over multiple years. Overall, the positive predictive value for the entire screen was 37%, consistent with the British study.
Only 80% of invasive ovarian cancers express significant quantities of CA12515
. Consequently, numerous biomarkers have been evaluated to complement or replace CA125. Using multiplex assays, some 96 biomarkers have been tested for the ability to distinguish healthy individuals from women with stage I ovarian cancer.20
A four biomarker panel that included CA125, human epididymous protein 4 (HE4), carcinoembryonic antigen (CEA) and soluble vascular adhesion molecule (sVCAM) produced 86% sensitivity for early stage (I/II) disease and 95% sensitivity for late stage (III/IV) disease at 98% specificity. Similar sensitivity and specificity were observed at the time of conventional diagnosis with the proteomic biomarkers evaluated in this study. A panel of Apo-A1, TT, and CTAPIII produced 87% sensitivity at 98% specificity for distinguishing stage I ovarian cancer from healthy individuals.7
The discrepancy in the results in pre-diagnostic samples for the three biomarker panel compared to our previous studies using post-diagnostic samples4,6
may relate to the fact that Apo-A1, TT and CTAPIII are each acute phase reactants that are down-regulated in response to cancer, and that a significant volume of tumor may be required to trigger this reaction. While stage I disease is by definition limited to the ovaries, the volume of cancer can be substantial, but must be sufficient to produce symptoms or a readily palpable pelvic mass to result in conventional diagnosis. In pre-clinical disease, the volume of tumor may not be sufficient to evoke an acute phase response, and alter levels of proteins associated with this process. Another issue with the markers in our panel (with the exception of CA125) is that they were lower in cancer cases, but also be reduced as a result of storage time, sample processing, and other host factors (described in our previous report) 6
which could hinder identification of small volume disease, a goal of the current study. Lastly, the current study clearly attempted to reduce confounding and bias in ways that were not possible in our previous study in which we matched cases to hospital controls rather than healthy women, and we were unable to control sample processing or match on storage time which may have biased results.
Although a marginally higher performance was observed for identification of cases at least six months prior diagnosis using an all-site multi-marker panel (that included CA125, HE4, tumor associated glycoprotein 72 (CA72-4), substance P-like immunoreactivity (SLPI) and β2M) were observed compared to CA125 alone, the increase was not statistically significant.21
In addition to the current study, five additional panels were evaluated, none of which improved upon results with CA125 alone8
. Considering the failure of multiple biomarkers to improve upon CA125 in pre-diagnostic samples, new approaches are badly needed for biomarker discovery. One weakness of the current study is that we were unable to evaluate markers in non-white populations due to a very small number of non-white cases in the PLCO Trial. The results of this combined effort will likely reshape our approach to biomarker discovery and validation. In addition to searching for protein analytes, auto-antibodies might also be sought. Lastly, previous studies have had limited success in identifying and evaluated auto-antibodies of human proteins expressed in bacteria or insect cells. Recent advances in expressing human proteins in human cells could allow identification of new epitopes that are selective for altered tertiary structure and glycosylation status of selected protein targets.