Validation of the predictive accuracy of health-state utility values based on the Lloyd model for metastatic or recurrent breast cancer in Japan

INTRODUCTION: Although there is a lack of data on health-state utility values (HSUVs) for calculating quality-adjusted life-years in Japan, cost–utility analysis has been introduced by the Japanese government to inform decision making in the medical field since 2016. OBJECTIVES: This study aimed to determine whether the Lloyd model which was a predictive model of HSUVs for metastatic breast cancer (MBC) patients in the UK can accurately predict actual HSUVs for Japanese patients with MBC. DESIGN: The prospective observational study followed by the validation study of the clinical predictive model. SETTING AND PARTICIPANTS: Forty-four Japanese patients with MBC were studied at 336 survey points. METHODS: This study consisted of two phases. In the first phase, we constructed a database of clinical data prospectively and HSUVs for Japanese patients with MBC to evaluate the predictive accuracy of HSUVs calculated using the Lloyd model. In the second phase, Bland-Altman analysis was used to determine how accurately predicted HSUVs (based on the Lloyd model) correlated with actual HSUVs obtained using the EuroQol 5-Dimension 5-Level questionnaire, a preference-based measure of HSUVs in patients with MBC. RESULTS: In the Bland-Altman analysis, the mean difference between HSUVs estimated by the Lloyd model and actual HSUVs, or systematic error, was −0.106. The precision was 0.165. The 95% limits of agreement ranged from −0.436 to 0.225. The t value was 4.6972, which was greater than the t value with 2 degrees of freedom at the 5% significance level (p=0.425). CONCLUSIONS: There were acceptable degrees of fixed and proportional errors associated with the prediction of HSUVs based on the Lloyd model for Japanese patients with MBC. We recommend that sensitivity analysis be performed when conducting cost-effectiveness analyses with HSUVs calculated using the Lloyd model.