Validation of time to treatment change (TTC) as a surrogate end-point of progression free survival (PFS) for observational trials in metastatic breast cancer patients (MBC): The GIM-13 AMBRA study.

e13081Background: Real-world studies (RWS) are crucial in clinical outcome evaluation of cancer patients (pts), however results are difficult to compare to randomized trials, mainly regarding time parameters, such as PSF, which is not the case in RWS. AMBRA is an observational study, aiming to describe the choice of first and subsequent lines of treatment in HER2-ve MBC pts receiving chemotherapy (CHT). One of the aims is the validation of TTC as a surrogate parameter of PFS. The present analysis is focused on the comparison between TTC and PFS of 1-line Paclitaxel + Bevacizumab (P+B) as an example of TTC in RWS. Methods: PFS was calculated using the progression dates declared by researchers. TTC was defined as the time between 1st line CHT start and the beginning of the subsequent therapy, if any, or the last observation or death. Since some pts could have changed therapy due to side effects, we considered a difference of ± 8 weeks acceptable. Results: Pts treated with P+B were 173/607 CHT (28.5%). Media...