Triaging women with ovarian masses for surgery: observational diagnostic study to compare RCOG guidelines with an International Ovarian Tumour Analysis (IOTA) group protocol

Abstract

Objective: To compare guidelines from the Royal College of Obstetricians and Gynaecologists (RCOG) based on the Risk of Malignancy Index (RMI) with a protocol based on logistic regression model LR2 developed by the International Ovarian Tumour Analysis (IOTA) group for triaging women with an ovarian mass as low, moderate, or high risk of malignancy.

Design and setting: Observational diagnostic study conducted between 2005 and 2007 at 21 oncology referral centres, referral centres for ultrasonography and general hospitals.

Sample: In all, 1938 women undergoing surgery for an ovarian mass.

Methods: RCOG guidelines use the RMI to triage women as low (RMI < 25), moderate (25-250), or high (above >250) risk. The IOTA protocol uses LR2s estimated probability of malignancy (<0.05 indicates low risk, ≥ 0.05 but <0.25 moderate risk, and ≥ 0.25 high risk).

Main outcome measure: Percentages of benign, borderline and invasive tumours classified as low, moderate or high risk.

Results: The IOTA and RCOG protocols classified 71.1% and 62.1% of benign tumours as low risk, respectively (difference 9.0; 95% CI 6.2-11.9, P < 0.0001). Of invasive tumours, 88.6% and 73.6% were labelled high risk (difference 15.0; 10.6-19.4, P < 0.0001), and 3.0% and 5.2% were labelled low risk (difference -2.2; -4.6 to 0.2, P = 0.07) respectively by each protocol. Similar results were found after stratification for menopausal status.

Conclusions: The IOTA protocol was more accurate for triage than the RCOG protocol. The IOTA protocol would avoid major surgery for more women with benign tumours while still appropriately referring more women with an invasive tumour to a gynaecological oncologist.