OC23.02: Which histologies limit the ability of CA‐125 to characterize adnexal masses? An observational study of 3511 patients

simple rules were not applicable. 649 of these masses had CA-125 results available. The malignancy rate was 31% (203/649). The data were randomly divided into a development set (70% of the data, n = 457) and a test set (30% of the data, n = 192). Results: In the development set, the following variables were retained as predictors of malignancy: age, personal history of ovarian cancer, largest diameter of the lesion, largest diameter of the largest solid component, presence of blood flow in papillary projection and CA125. The area under the ROC curve (AUC) was 0.86 (95% CI, 0.82–0.90) in the development set and 0.83 (0.76–0.89) in the test set. Expert’s subjective assessment and RMI had an AUC in the test set of 0.88 (0.82–0.94) and 0.69 (0.60–0.77), respectively. To be able to compare the performance of the new model with LR1 and LR2, we excluded from the test set the 53 cases that were part of the original development set for LR1 and LR2 (IOTA phase 1, 1999–2004). On the reduced test set of 139 cases, the AUC of the new model, subjective assessment, RMI, LR1 and LR2 were 0.83 (0.76–0.91), 0.87 (0.80–0.94), 0.72 (0.63–0.81), 0.79 (0.71–0.87) and 0.72 (0.63–0.82), respectively. Conclusions: In adnexal masses where the simple rules are not applicable, our new mathematical model might be useful, but its performance must be prospectively validated.