Performance of time to discontinuation and time to next treatment as proxy measures of progression-free survival overall and by treatment group
Real-world data sources have historically provided limited information about the occurrence of disease progression. As a result, progression-free survival (PFS), a standard effectiveness outcome measure in oncology, has been estimated using proxies such as time-to-discontinuation (TTD) or time-to-next-treatment (TTNT). Curation of unstructured electronic medical record (EMR) data make it possible to calculate PFS from directly observed progression. The aim of this research was to compare TTD and TTNT as proxy indicators with PFS determined from direct statements regarding progression in the medical record and to compare effect sizes on treatment-based groups across these endpoints. This study showed that estimates of TTD and TTNT aligned closely, suggesting that nearly all patients who discontinued initial therapy received subsequent treatment. Notably, TTNT and TTD were both meaningfully shorter than PFS, suggesting that their use as proxy indicators may systematically underestimate PFS. Further, analysis based on receipt of AI indicates that comparative effects on TTD or TTNT may produce quite different results than those for PFS and OS.