The ability to detect human malignancy by a simple blood test has long been an objective in medical screening. A suitable test or examination to screen for a disease should have both high sensitivity (the probability of the test being positive in individuals with disease) and high specificity (the probability of the test being negative in those without the disease). Developing a highly specific screening test is a major concern for ovarian cancer because the majority of women who test positive on screening will require surgery to confirm the diagnosis. A screening test with low specificity requires a large number of operations to detect one case of ovarian cancer, which is not acceptable to
patients or their doctors. For example, in postmenopausal women, even a screening test with 98% specificity would result in operations on 50 women who do not have cancer for every one case of ovarian cancer found during surgery.
Because the incidence of ovarian cancer in the general population is low, approximately 1.8%, the specificity of the CA-125 blood test (a test currently used for ovarian cancer) is unacceptably low for screening for ovarian cancer in the general population.