OBJECTIVES: Endpoints based on the assessment of the tumour include progression-free survival (PFS), Time to Progression (TTP) and overall survival (OS). While OS measures survival time in general, PFS includes tumour progression assessment in addition to survival time. Discussions arose on whether to use both endpoints in clinical trials and whether patients differentiate between them.

METHODS: The study aimed to quantify patients preferences for both endpoints of treatments in women with advanced or metastatic breast cancer in Germany. Within a discrete choice experiment the interaction between OS and TTP was modelled as a two-dimensional compound attribute defined by six levels to represent the impact on preferences of a change in TTP at different levels of OS.

RESULTS: ‘TTP/OS’ was the most important favourable effect with the highest relative importance for N=233 patients with advanced or metastatic breast cancer. The compound attribute was consistent with the expected ordering of the categories; e.g.50-month OS is rated higher at 5 months without progression than 30 months OS/25 months without progression. “25 months without progression/30 months OS” is rated equally to “5 month without progression/40 month OS”. Respondents always preferred higher TTP to a lower TTP independent of the level of ‘OS’. When keeping OS constant, TTP was shown to independently impact treatment choices by respondents.

CONCLUSIONS: Suitability of PFS as surrogate endpoint is controversial. This study revealed that compound attributes may represent a possible approach to document the value of TTP. The value to patients can be demonstrated independently of the causal relationship between these two trial endpoints. Changes in the level of TTP positively impacted respondents’ choices independent of OS. Hence, TTP can be seen as an independent decisive factor.