- To provide a large database of pre-operative CA 125 levels which may predict inappropriate cytoreductive surgery in patients with advanced epithelial ovarian cancer. A multicenter review of the records of 424 patients with FIGO stage III and IV epithelial ovarian cancer of patients who underwent primary cytoreductive surgery was performed. The validity of pre-operative CA 125 level measurement as a single predictor of the possibility to achieve only suboptimal cytoreduction was evaluated by calculating the sensitivity and the specificity of various cut-off values. The relative importance of different cut-off values in achieving the best predictive validity was assessed by a receiver operating characteristics (ROC) curve. Optimal cytoreduction (largest diameter of residual tumour < or =1 cm) was achieved in 242 patients. The median CA 125 level in optimally cytoreduced patients was lower than in those patients suboptimally debulked (304 vs 863 U/mL; p<0.001). The area under the ROC curve was 0.65 (95% confidence interval, 0.60-0.71) and the CA 125 threshold derived from the ROC was 400 U/mL. The accuracy of the test at this level was 62%. The clinical applicability of the ROC derived CA 125 threshold is limited. The data accrued in the study provides a basis for decision-making regarding the place of primary surgery various CA 125 levels.