External multicentre validation of a nomogram predicting the risk of relapse in patients with borderline ovarian tumours

Background: The Obermair nomogram was recently developed to predict the risk of relapse in patients with borderline ovarian tumours (BOTs) based on five readily available clinical, biological, and pathological characteristics. We set out to externally validate and assess its robustness using a multi-institutional BOT database. Methods: All consecutive patients treated for BOTs in the two participating centres between January 1980 and December 2008 and who had all the nomogram variables documented were identified for analysis. Results: Three hundred and fourteen eligible patients were identified and used for external validation analysis. The median follow-up and initial relapse time were 46.43 (range: 0.1-360) and 66.64 (range: 8-77) months, respectively. The nomogram concordance index was 0.54 (95% CI, 0.52-0.56). The correspondence between the actual relapse and the nomogram predictions suggests a limited calibration of the nomogram in the validation cohort. Conclusion: This external validation study of the Obermair nomogram showed limitations in its generalisability to a new and independent patient population.