The diagnostic value of multimodality MRI in endometrial carcinoma staging: methodological issues to avoid misinterpretation

I have with interest read the paper by Du and colleagues published in Acta Radiologica in May 2017 (1). Multimodality magnetic resonance imaging (MRI) can determine the stage of endometrial carcinoma by providing a guidance for selection of surgical treatment and postoperative prognostic assessment. MRI has an important role in improving the survival of patients with endometrial carcinoma. The purpose of the authors was to evaluate multimodality MRI staging accuracy for endometrial carcinoma based on the International Federation of Gynecology and Obstetrics (FIGO 2009) staging system (1). They retrospectively studied the complete clinical and surgical pathology data from 83 patients with endometrial carcinoma treated between June 2011 and August 2015. Using a blinded design, the preoperative clinical staging according to the current FIGO 2009 MRI-based staging was analyzed and correlated with postoperative histopathological results, which served as the staging standard (1). Based on their results, multimodality MRI staging accuracy for endometrial carcinoma stages I–IV by FIGO 2009 were 91.6% (76/83), 91.6% (76/83), 92.8% (77/83), and 97.6% (81/83), respectively (1). However, this result is not the most appropriate estimate to assess diagnostic accuracy. Diagnostic value can be considered as diagnostic accuracy (validity) and diagnostic precision (reliability). To assess validity, for qualitative variables, sensitivity, specificity,) positive predictive value (PPV), negative predictive value (NPV), likelihood ratio positive, and likelihood ratio negative as well as diagnostic accuracy and odds ratio (ratio of true to false results) are among the most appropriate and complete estimates. However, for clinical purposes, it is crucial to know that reporting diagnostic added value of a diagnostic test should be considered because the above validity estimates can be acceptable (as in this paper) while diagnostic added value may be negligible (2–6). This can be easily done by using receiver operating characteristic (ROC) curve. Reliability (precision) as a different methodological issue of diagnostic value should also be assessed by appropriate estimates. For qualitative variables, applying kappa is one of the methodological mistakes. Two important weaknesses of k value to assess agreement are as follows: it depends upon the prevalence in each category. It is possible to have different kappa values having the same percentage for both concordant and discordant cells. Kappa value also depends upon the number of categories. Therefore, in such a situation, weighted kappa should be applied with caution (2–6). Without assessing precision, we cannot judge about the diagnostic value of the multimodality MRI. The authors concluded that the current FIGO staging system appears to be a concise, reasonable, and practical set of criteria for the clinical management of endometrial carcinoma. Such a conclusion should be supported by the abovementioned statistical and methodological issues. Otherwise, in clinical practice, misdiagnosis and mismanagement of the patients may occur.