Prospective study of serum CA-125 levels as markers of ovarian cancer.

OBJECTIVE

To evaluate prospectively the sensitivity and specificity of serum CA-125 levels for the detection of ovarian cancer.

DESIGN

Case-control study nested within a cohort of women who donated blood to a community-based serum bank established in 1974.

SETTING

Washington County, Maryland.

POPULATION

Cases consisted of 37 women who developed ovarian cancer from 1975 through 1989. Controls consisted of 73 women, matched on age and time since last menstrual period, and free of cancer until the cases' diagnoses. STUDY VARIABLE: Serum CA-125 levels.

OUTCOME MEASURE

Histologically confirmed ovarian cancer.

RESULTS

Levels of serum CA-125 among cases were higher than among controls for each 3-year interval up to 12 years prior to the time of the cases' diagnoses. The median level for cases diagnosed within the first 3 years of follow-up was 35.4 U/mL compared with 9.0 U/mL for controls (P = .002). The sensitivity of a serum CA-125 level greater than 35 U/mL within the first 3 years was 57% (95% confidence interval, 20% to 88%) and the specificity was 100% (95% confidence interval lower limit, 73%). Sensitivity and specificity decreased with increasing time to diagnosis.

CONCLUSIONS

Measurement of serum CA-125 levels, particularly at a reference value of 35 U/mL, is not sufficiently sensitive to be used alone as a screening test for the detection of ovarian cancer. Lower CA-125 reference values could identify women at higher risk of developing ovarian cancer, but CA-125 measurement cannot be recommended for this purpose because of the high proportion of women who would be falsely classified as being at high risk for developing ovarian cancer.