Ovarian cancer early detection by circulating CA 125 in the context of anti‐ CA 125 autoantibody levels: Results from the EPIC cohort

CA125 is the best ovarian cancer early detection marker to date; however, sensitivity is limited and complementary markers are required to improve discrimination between ovarian cancer cases and non‐cases. Anti‐CA125 autoantibodies are observed in circulation. Our objective was to evaluate whether these antibodies (1) can serve as early detection markers, providing evidence of an immune response to a developing tumor, and (2) modify the discriminatory capacity of CA125 by either masking CA125 levels (resulting in lower discrimination) or acting synergistically to improve discrimination between cases and non‐cases. We investigated these objectives using a nested case–control study within the European Prospective Investigation into Cancer and Nutrition cohort (EPIC) including 250 cases diagnosed within 4 years of blood collection and up to four matched controls. Circulating CA125 antigen and antibody levels were quantified using an electrochemiluminescence assay. Adjusted areas under the curve (aAUCs) by 2‐year lag‐time intervals were calculated using conditional logistic regression calibrated toward the absolute risk estimates from a pre‐existing epidemiological risk model as an offset‐variable. Anti‐CA125 levels alone did not discriminate cases from controls. For cases diagnosed