Page 60 - The diagnostic work-up of women with postmenopausal bleeding

Chapter 3
can conclude that although these models do not show a high AUC, they could be useful in clinical practice.These models were found to discriminate women with a high risk for endometrial cancer from women with low risk and to select women for further (invasive) testing.
The conclusions above are based on reported model performance based on internal validation only.To implement a prediction model into clinical practice, external validation is essential. McGinn et al describe three reasons.25 A prediction model may reflect associations between given predictors and outcomes that are primarily due to chance. Secondly, the predictor variables used in a model may be idiosyncratic to that specific population, which suggests that the prediction model may fail in a new setting. And thirdly, clinicians may fail to implement the model comprehensively or accurately in their clinical practice.The result would be that a model succeeds in theory, but fails in practice. For a successful implementation, a model should be validated both internally and externally and finally go through the phase of impact analysis in the same population in which a model is derived. As none of the prediction models have completed the phase of external validation, they cannot be used in clinical practice yet.
When evaluating these prediction models by external validation or finally in impact analysis, one should keep in mind that these models were developed in different patient populations. The target population in which a model is derived should be the same as the population in which a model is tested or clinically used. Selecting a high-risk population (for example, a population with an ET 5mm) will result in a different performance and possibly in the selection of different predictor variables compared to an unselected population of women with PMB. Furthermore, in an unselected population there could be implicate selection dependent of a population within a general practice or a population within a gynaecological practice or differences in health systems in different countries. Different populations have different prevalence of endometrial cancer, which could be an explanation for the differences found in the performance of the models.A consensus has not been found in systematic reviews or in international guidelines regarding the best sequence of diagnostic procedures for women with PMB.9 Considering the performance of the existing prediction models, we can conclude that we have indications that the first step in the approach of women with PMB should be to distinguish between women with low versus increased risk of having endometrial cancer and the next step would be to refer patients forTVS or further invasive testing.
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