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Overall survival (OS) in metastatic breast cancer (MBC): Are we using the right endpoint in the right way?

142 Background: OS has been historically considered the most important clinical endpoint in MBC trials; however survival could be influenced by treatment after progression in an era of effective subsequent-line agents.


METHODS
We conducted a search strategy using PubMed for randomized phase 3 trials published in the last 2 decades (1994-2014) evaluating survival outcome in MBC. We investigated the frequency of trials reporting post progression outcome and response/resistance to treatment beyond progression.


RESULTS
110 trials met our eligibility criteria: 69 (63%) evaluated chemotherapy regimens (group A), 27 (25%) evaluated targeted therapy (group B) and 14 (13%) focused on endocrine treatment (group C). The majority of the trials had OS as a primary or secondary endpoint (97% (66/69), 100% (27/27) and 86% (12/14) of the trials in group A, B and C respectively). An OS benefit was demonstrated in approximately 22% of the trials in each group. Post progression survival (PPS) and its effect on OS was reported and discussed in only 1% (1/69), 4% (1/27) and 7% (1/14) of the trials for group A, B and C respectively. Less than 10% of the trials in group A and B reported response data and duration of response after progression on trial therapy. In addition, post progression treatment resistance was only reported in group A in 3% (2/69) of the trials. Furthermore, the number of lines of treatment used post progression was reported in only 14% (10/69), 11% (3/27) and 14% (2/14) of the trials in group A, B and C respectively.


CONCLUSIONS
A clear paucity of post progression treatment information is noted in the majority of the phase 3 trials for MBC. We do know that OS is directly affected by treatments used after progression. In order to assess the true clinical benefit of a new drug and a complete evaluation of overall survival outcome, a detailed collection of post progression treatment information is required and should be mandated in MBC clinical studies.