IntroductionPelvic masses are among most the common causes of patient admission into gynecology clinics and one of the most common reasons for referral to gynecologic oncology departments due to the risk of uterine or ovarian malignancies. The aim of this study is to compare the four indices of the risk of malignancy index (RMI 1–4), as a combination of menstrual status, radiological findings, and serum CA125 concentration, for discrimination of benign from malignant pelvic masses.MethodsThis retrospective descriptive and analytic study was conducted on 200 patients with pelvic mass, post-surgery, and who were referred to the oncology department in Shahid Sadoughi hospital of Yazd (Iran) between June 2007 and September 2011. Data regarding demographics, pathology reports, paraclinical and clinical tests were analyzed. The four RMI indices were separately used for determination of benign vs. malignant masses using the optimized cutoff points, ROC curve, sensitivity, specificity, predictive value of positive and negative, and accuracy. Finally, p value for each index was calculated, and a final discrimination power was measured by using SPSS version 17 software.ResultsThe calculated p values in the four RMI indices in ultrasound findings indicated statistical significance, and the RMI 2 showed the highest level of accuracy or diagnostic performance. RMI 2 had a cutoff point of 90, an under-chart area 86.7, 79.36% sensitivity, 78.95% specificity, 58.44%, positive predictive value, 90.08% negative predictive value, and 78.93% accuracy, and a p value of 0.004. However, this relationship was found not to be meaningful using CT scan images.ConclusionsUsing RMI 2 for differentiation of malignant from benign pelvic masses is a reliable method with ultrasound findings.