Combining a Symptoms Index With CA 125 to Improve Detection of Ovarian Cancer

Abstract

BACKGROUND

The current study sought to examine whether an index based on the specific pattern of symptoms commonly reported by women with ovarian cancer could be used in combination with CA 125 to improve the sensitivity or specificity of experimental methods of screening for ovarian cancer.

METHODS

A prospective case-control study design was used. Participants included 254 healthy women at high risk for disease because of family history, and 75 women with ovarian cancer. Logistic regression analysis was used to determine whether the symptom index predicted cancer.

RESULTS

Symptom index information was found to make a significant independent contribution to the prediction of ovarian cancer after controlling for CA 125 levels (P <.05). The combination of CA 125 and the symptom index identified 89.3% of the women with cancer, 80.6% of the early-stage cancers, and 95.1% of the late-stage cancers. The symptom index identified cancer in 50% of the affected women who did not have elevated CA 125 levels. Unfortunately, 11.8% of the high-risk women without cancer also received a positive symptom index score.

CONCLUSIONS

The addition of a symptom index to CA 125 created a composite index with a greater sensitivity for the detection of ovarian cancer than CA 125 alone and identified >80% of women with early-stage disease. A composite marker such as this could serve as a first screen in a multistep screening program in which false-positive findings are identified via transvaginal sonography before referral for surgery, leading to an adequate positive predictive value for the multistep program.

Ovarian cancer is the second most common gynecologic malignancy in the U.S. Greater than 70% of women with ovarian cancer are diagnosed with advanced stage disease, in which the cure rates are only 20% to 30%, making it also the most deadly cancer.¹ Fortunately, cure rates for those diagnosed when the disease is confined to the ovary are approximately 70% to 90%.² Historically, the symptoms of ovarian cancer were thought to develop only after the disease had progressed to an advanced stage. However, recent research has shown that many women with early-stage disease report symptoms and the report of 1 of 3 symptoms that are new to an individual and occur frequently in ovarian cancer may serve to distinguish cancer cases from healthy women.^3–5

Although ovarian cancer meets the World Heath Organization’s criteria of a disease that would benefit from screening,⁶ our current screening modalities have not been shown to reduce the morbidity or mortality of this disease. Currently, the American College of Obstetricians and Gynecologist and the U.S. Preventative Services Task Force recommend against screening for ovarian cancer in average-risk women. The National Institutes of Health (NIH) Consensus Panel on Ovarian Cancer statement also indicated that although currently available screening tests (CA 125 and transvaginal ultrasound [TVS]) should not be used for screening average-risk women outside of research trials, women with a family history of ovarian cancer (ie, those considered to be at an elevated risk) could reasonably choose to pursue screening using CA 125 and TVS. Despite uncertainty regarding the effectiveness of screening using current tests, screening for ovarian cancer was and is encouraged for those women at high risk for ovarian cancer because of a possible BRCA1/2 mutation and who have not chosen to pursue surgical risk reduction.⁷ Recently, a consensus statement concerning symptoms has come out to encourage the evaluation of ovarian cancer for women with certain symptoms associated with this disease.

The effectiveness of several multimodal screening strategies for ovarian cancer using biomarkers (often CA 125) and TVS currently are being studied in several trials.^8,9 These strategies generally include the annual (or more frequent) evaluation of blood biomarkers that might indicate the presence of a cancer. In these studies, TVS is generally a second screening tool for women who have positive biomarker results. Screening programs may or may not include the annual routine use of TVS as a first-line screen. Unfortunately, to our knowledge it is unclear how successful these various strategies for screening will be. Although TVS is a very sensitive test, when used as a first-line screen it produces a relatively high rate of false-positive results that require surgical follow-up and a rate of surgeries-per-cancer found that is unacceptable to most clinicians.¹⁰ When blood biomarkers are used for first-line screening, women with positive results generally do not go directly to surgery. Instead, TVS is generally used as a second screening step to identify women with false-positive marker results before surgical referral. When TVS is used as a second level of screening, the sensitivity of the multimodal screening program as a whole is limited by the sensitivity of the initial screening biomarker used. CA 125 has been used for this purpose. Unfortunately, CA 125 is elevated above reference levels in only approximately 50% of patients with clinically detectable, early-stage disease.^2,11,12 Statistical efforts currently are under way to improve the performance of CA 125,¹³ as are studies of markers to be used in combination with CA 125 to trigger TVS as a second-stage screening test.^14–16 Using a combination of markers to create a composite marker for use as an initial screen could improve the diagnostic performance of a 2-step screening program. In addition, the positive predictive value (PPV) of the screening program could be assured by the use of a second test such as TVS that would identify the majority of the false-positive results among the initial screening results. Efforts to combine CA 125 with other markers have included examinations of CA 125 with HE4, mesothelin, and other markers.^14–17 Mesothelin^18–21 and HE4^22,23 may be 2 of the most promising new ovarian cancer biomarkers currently under evaluation. Their diagnostic performance is known and they appear to complement CA 125. Briefly, mesothelin is an epithelial biomarker¹⁴ and HE4 is commonly found to be overexpressed in ovarian cancer tissue and elevated in the serum of patients with ovarian cancer.^22–24

The current study presents a second report on the results of a study seeking to create a symptom index that could be used to differentiate women with undiagnosed ovarian cancer from healthy women and those with other gynecologic conditions. The prior report described the development of a symptom index in an exploratory dataset and analysis of the sensitivity and specificity of that index in a confirmatory dataset and with a general clinic control group.⁵ The symptom index thus developed consists of a decision-rule to be used in determining whether symptoms reported by a woman might suggest that she has ovarian cancer. Women reporting symptoms of pelvic or abdominal pain, bloating, increased abdominal size, difficulty eating, or feeling full quickly >12 times per month that have occurred for < 1 year are considered to have a positive symptom index.⁵ Few women (approximately 2%) in a general clinic sample report symptoms consistent with a positive index score. This report builds on our prior research by determining whether symptom reports might make an independent contribution to the prediction of ovarian cancer in a screening situation when data are also available on CA 125. We hypothesized that the symptom index would identify women with cancer who do not have elevated levels of CA 125 but might benefit from immediate TVS evaluation, and thus might add to the sensitivity of CA 125 and/or other biomarkers as an initial screening marker in a multistep screening strategy.

MATERIALS AND METHODS

Approval for this study was obtained from the Institutional Review Board of the Fred Hutchinson Cancer Research Center and area hospitals with participating patients. All women provided informed consent.

Study Population

The sample of women examined in this report consists of a subgroup of the women participating in prior studies.^3,5 This includes women undergoing surgery for pelvic masses who were later diagnosed with ovarian cancer (our case group), and a screening control group comprised of women enrolled in a high-risk screening program, the Ovarian Cancer Early Detection Study (OCEDS).³ Because women were ineligible if they had already received a diagnosis of ovarian cancer before surgery, our case group included a larger than might be expected proportion of women with early-stage disease. Women in OCEDS may or may not have a BRCA1/2 mutation but have high-risk family histories consistent with a possible BRCA1/2 mutation in their families. This report includes those women who volunteered to donate blood for assessment of their CA 125 blood levels for research purposes as part of their participation in the prior study. All participants also completed surveys asking about the frequency (number of days per month) and the duration (number of months) of several symptoms.³

High-risk women participating in a screening program were considered to be a valuable control group for the current analysis because they may present a challenge for a method of ovarian cancer detection reliant on self-reported symptoms. Such women are likely to have an increased awareness of ovarian cancer and may be highly sensitive to and report symptoms believed to be associated with ovarian cancer more frequently than women who are less aware of their risk. In the screening population, surveys were completed as part of ovarian cancer screening visits conducted on a quarterly basis. In the surgical population, all women were surveyed before surgery before receiving a definitive diagnosis of ovarian cancer.

Blood Collection and Processing

Blood was collected for the assessment of CA 125 levels according to a consistent protocol. Blood samples sat at room temperature for at least 30 minutes after collection and before processing to allow clotting. Samples were centrifuged for at 1200g for 10 minutes. The serum was then collected and stored at −80°C.

Determination of the Stage of Disease at Diagnosis

Women with ovarian cancer diagnosed at stages I or II were considered to have early-stage disease. Those diagnosed at stages III or IV were considered to have late-stage disease (determined according to the International Federation of Gynecology and Obstetrics staging system).

Laboratory Analysis

Antibodies

CA 125 levels were assessed using bead-based immunoassays performed as described in Scholler et al.¹⁶ This procedure has been described elsewhere and found to yield values that are strongly correlated (correlation coefficient [r] > 0.90) with the research standard CA 125II RIA from Fujirebio Diagnostics (FDI, Malvern, Penn).¹⁶

CA 125 levels and the symptoms index

The threshold for a positive CA 125 test was determined by dichotomizing CA 125 at the 95th percentile in the screening control group. Cases and controls with a CA 125 level above this threshold were considered to have a positive CA 125 test. Because CA 125II RIA values were available for the screening control group, the cutoff value was calculated and found to be approximately 30 U/mL.

Consistent with the symptom index as previously described,⁵ women were classified as having a positive symptom index if they reported any of the following symptoms >12 times per month, occurring only within the past 12 months: bloating or increased abdominal size, abdominal or pelvic pain, and difficulty eating or feeling full quickly.

Statistical Analysis

The STATA statistical software package (version 9.0; StataCorp, College Station, Tex) was used for the analyses in this study. All statistical tests were 2-sided and considered to be statistically significant at P ≤ .05. Baseline age was dichotomized at 50 years. The age, stage, dichotomized CA 125 levels, symptom index, and results of the 2 markers used in combination were compared across the study populations using the chi-square test. Combinations of the 2 markers examined included an ‘‘either’’ combination in which a woman was considered positive if she had either a positive CA 125 index or a positive symptoms index. Combinations were also examined in which a woman was considered to have a positive marker only if both the symptoms index and the CA 125 were positive. Unconditional logistic regression analysis was used to determine whether the symptom index independently predicted cancer after controlling for CA 125.

The diagnostic accuracy of the dichotomized CA 125 levels, symptom index, and both combinations of the 2 were then determined by calculating the sensitivity (true-positives/true-positives + false-negatives), and specificity (true-negatives/true-negatives + false-positives) of each. The sensitivity and specificity of the symptom index, CA 125 blood test, and their uses in combination were also calculated for women aged ≥50 years and those aged < 50 years. The sensitivity of each index was calculated for those with early-stage and late-stage disease.

RESULTS

There were 75 cases from the surgical population included in the current analysis and 254 controls from the screening population. Cases were more likely to be older (P <.001), have a positive CA 125 value (P <.001), and to have a positive symptom index (P <.001) than those in the screening control group (Table 1). As illustrated in Table 2, greater than half of the cancer cases (53.3%) were both symptom index-positive and had an elevated CA 125 level, 25.3% had only an elevated CA 125 level, and 50% of the remaining cases (10.7% of the total case group) could be identified by a positive symptom index score only.

TABLE 1.

Age, Stage, and Index Scores by Population

	Controls (n = 254)	Cases (n = 75)	P
Age, y* no. (%)
< 50	122 (49.6)	13 (18.1)
≥50	124 (50.4)	59 (81.9)	< .001
Stage,† no. (%)
Early	NA	31 (43.1)
Late	NA	41 (56.9)
CA 125,‡ no. (%)
Positive CA 125	12 (4.7)	59 (78.7)
Negative CA 125	242 (95.3)	16 (21.3)	< .001
Symptoms index,§ no. (%)
Positive symptoms index	30 (11.8)	48 (64.0)
Negative symptoms index	224 (88.2)	27 (36.0)	< .001
Composite marker,|| no. (%)
Positive combined index	42 (16.5)	67 (89.33)
Negative combined index	212 (83.5)	8 (10.67)	< .001

NA indicates not applicable.

^*Data were missing for 8 subjects in the high-risk screening population and 3 cases.

^†Data were missing for 3 cases.

^‡CA 125 dichotomized at the 95th percentile in the screening population. Subjects with a CA 125 value above that threshold were considered to have a positive CA 125 index.

^§The symptoms index was considered positive if the patient had 1 of the following symptoms for < 1 year but it occurred >12 times per month: bloating or increased abdominal size, abdominal or pelvic pain, difficulty eating, or feeling full quickly.

^||The composite marker was considered positive if the patient had either a positive CA 125 index or a positive symptoms index (or both).

TABLE 2.

Frequency (%) of Positive Index Results for CA 125,^* the Symptoms Index^†, and Combinations of the 2

Test Results	Controls (n = 254)	Cases (n = 75)
Negative for both the symptoms index and CA 125	212 (83.5)	8 (10.7)
Negative for the symptoms index but positive for CA 125	12 (4.7)	19 (25.3)
Positive for the symptoms index but negative for CA 125	30 (11.8)	8 (10.7)
Positive for both the symptoms index and CA 125	0	40 (53.3)

^*CA 125 dichotomized at the 95th percentile in the screening population. Subjects with a CA 125 value above that threshold were considered to have a positive CA 125 index.

^†The symptoms index was considered positive if the patient had 1 of the following symptoms for < 1 year but it occurred >12 times per month: bloating or increased abdominal size, abdominal or pelvic pain, difficulty eating, or feeling full quickly.

Results from the logistic regression indicated that the symptom index independently predicted cancer after adjusting for CA 125 levels (odds ratio [OR] of 11.51; 95% confidence interval [95% CI], 4.62–28.66). As illustrated in Table 3, when used alone, the sensitivity of the symptom index was lower than the sensitivity of CA 125 (64.0% and 78.7%, respectively). However, a decision rule based on either CA 125 or the symptom index identified 89.3% of the cancers (80.6% of women with early-stage tumors and 95.1% of those with later-stage disease). These results suggest there is improved sensitivity associated with using the 2 markers in combination such that if either is positive it is an indication for immediate further evaluation. If used as screening without such a second step, the high sensitivity but low specificity associated with this combination would be problematic. However, the combination may be beneficial over the use of CA 125 alone when a second level of screening is planned because it identified a modest-sized group of women for more thorough evaluation, including a greater percentage of those with cancer. In the screening group, 16.5% of the women would have received an abnormal initial marker result and been referred for further evaluation using TVS. In fact, in this screening program all women received TVS annually because of their high-risk status.

TABLE 3.

Diagnostic Accuracy of Ovarian Cancer Screening Tests by Age and Stage (95% CI)

Screening tests	Sensitivity	Specificity
CA 125*	78.7 (76.7–87.3)	95.3 (91.9–97.5)
Age < 50 y	84.6 (54.6–98.1)	97.6 (93.1–99.5)
Age ≥50 y	78.0 (65.3–87.7)	93.4 (87.5–97.1)
Early stage	64.5 (45.4–80.8)	95.3 (91.9–97.5)
Late stage	90.2 (76.9–97.3)	95.3 (91.9–97.5)
Symptoms index†	64.0 (52.1–74.8)	88.2 (83.6–91.9)
Age < 50 y	84.6 (54.3–98.0)	88.5 (81.5–93.6)
Age ≥50 y	57.6 (44.1–70.4)	88.7 (81.8–93.7)
Early stage	45.2 (27.3–64.0)	88.2 (83.6–91.9)
Late stage	78.0 (62.4–89.4)	88.2 (83.6–91.9)
Composite marker‡	89.3 (80.1–95.3)	83.5 (78.3–87.8)
Age < 50 y	92.3 (64.0–99.8)	82.0 (74.0–88.3)
Age ≥50 y	88.1 (77.1–95.1)	86.3 (79.0–91.8)
Early stage	80.6 (62.5–92.5)	83.5 (79.3–87.8)
Late stage	95.1 (83.5–99.4)	83.5 (79.3–87.8)

95% CI indicates 95% confidence interval.

^*CA 125 dichotomized at the 95th percentile in the screening population. Subjects with a CA 125 value above that threshold were considered to have a positive CA 125 index.

^†The symptoms index was considered positive if the patient had 1 of the following symptoms for < 1 year but it occurred >12 times per month: bloating or increased abdominal size, abdominal or pelvic pain, difficulty eating, or feeling full quickly.

^‡The composite marker was considered positive if the patient had either a positive CA 125 index or a positive symptoms index (or both). Sensitivity = true-positives/(true-positives + false-negatives). Specificity = true-negatives/(true-negatives + false-positives).

Excellent specificity in the screening controls would have been obtained if the 2 markers were used in such a way that a woman was considered to have an abnormal initial screening result only if both CA 125 and the symptoms index were positive. This combination of the markers produced no false-positive results but was found to be positive in only 53% of the women with ovarian cancer (Table 2). Such a strategy for initial screening would have very good specificity, although the sensitivity would be quite modest.

DISCUSSION

Several retrospective studies using chart reviews have reported that a large percentage of women with ovarian cancer report symptoms before diagnosis.^25,26 Our studies^4,5 and those of others^25,27 have found significant differences in symptom reports between ovarian cancer patients and controls. As has been previously reported by Goff et al.,⁵ we have found that the report of specific symptoms associated with bloating, pain, and difficulty eating experienced frequently (>12 days a month) and new to a woman (beginning within the past 12 months) can be used to create a symptoms index that appears to identify women with yet-to-be diagnosed ovarian cancer.⁵

Efforts to identify effective and efficient screening programs using proteomic and other biomarkers continue to provide promising findings, but technical difficulties delay the reproducibility of new biomarkers.⁵ Thus, CA 125 continues to be studied as an initial screening test for ovarian cancer in experimental multimodal multistep screening programs. In these experimental screening programs, women with elevated CA 125 levels generally undergo further evaluation using TVS. Although CA 125 is a very good marker for detecting ovarian cancer reoccurrences, its overall sensitivity in early-stage disease is not ideal. This limits the sensitivity of multistep programs if it is used as an initial screening tool. As research on various screening strategies continues, symptoms may prove a valuable means of identifying a group of women who, in the absence of a positive CA 125 result, may have ovarian cancer and who might benefit from further evaluation using TVS. Under such circumstances, in which additional evaluation before surgery using a test-like TVS is planned, high rates of sensitivity would be very valuable so long as the specificity of a combined marker was reasonable because the PPV of the program as a whole would be the result of both steps of the screening process.

The result of the current analysis suggests that women who report the symptoms included in our index might profitably be evaluated using diagnostic tests such as TVS, even in the absence of an elevated CA 125 level. Such a response would be consistent with the recent recommendations of the consensus statement of ovarian cancer symptoms but was not clinic practice at the time of the current study. When used in combination with CA 125 as a first-line screening tool, the symptoms index identifies more women with ovarian cancer than CA 125 alone. This increase in sensitivity is achieved at some cost in specificity. The reduced specificity would be unfortunate if a second test were not being used to prevent unnecessary surgeries; however, with such a second-stage test available the increased sensitivity might prove useful as part of a multimodal effort to improve the early detection of ovarian cancer.

To our knowledge to date, screening has not been associated with the detection of disease at early stages. In a study by Liede et al.,²⁸ women at elevated risk were screened annually with examinations, CA 125, and TVS. During the study period, 6 of the 8 cancers diagnosed were found to be in advanced stages. In another study of 4526 women at elevated risk for ovarian cancer, TVS was performed every 6 months. During the study period there were 10 ovarian, fallopian tube, and primary peritoneal cancers, all of which were diagnosed in advanced stages.²⁹

In average-risk women, the incidence of ovarian cancer is 40 per 100,000 population. With this relatively low incidence, a screening test would need a specificity of 99.6% to achieve a PPV of 10%. To our knowledge, a cost-effective test that does not result in a low PPV and excessive morbidity from unnecessary surgery has yet to be developed. However, a multimodal screening approach would likely have a good PPV and result in very few surgeries per case found if symptomatic average-risk women were referred for CA 125 and/or other blood screening tests and TVS and were only referred for surgery when those screening tests were positive. It should be noted that there are limitations to the current study. Any recommendations regarding the possible uses of the symptom index as a potential screening tool should be approached with caution. Our results describing the symptom index are limited to data collected from a single group of cases participating in a single study. These women might be more inclined to report symptoms because they were being approached during their presurgical assessment and after it had been determined that they likely had some form of abdominal mass, although it was not yet known whether the mass was malignant or benign. Additional research in this area is needed, including independent collection of symptom data from women with and without cancer and a pilot study of the effects of using this symptom index prospectively to identify women for diagnostic testing for ovarian cancer.