Independent External Validation of the METSSS Model Predicting Survival After Palliative Radiotherapy

A validation of the recently published METSSS model (developed from a large US database) predicting survival after palliative radiotherapy was performed. METSSS includes age, sex, cancer type, localization of distant metastases, comorbidity, and radiotherapy site.

Both 1- and 5-year survival was assessed in the validation cohort. Deviations between model-predicted and observed survival were analyzed.

The METSSS model predicted a 1-year survival of 29% (cohort median, predicted probability 0-74% in individual patients). The observed 1-year survival rate was 33% (median survival 5.3 months). The corresponding figures for predicted 5-year survival were 0% and 0-46% (observed rate 3%). Statistical comparison of the survival curves was possible for two of three strata (insufficient number of low-risk patients) and the resulting p-value was 0.045.

A complete validation was hampered by imbalances in group size. More than 90% of our patients were classified as high risk. If this distribution is representative for other countries, the METSSS model might need adjustment. However, its general ability to predict survival appears promising.