Objectives: A primary outcome in oncology trials is overall survival (OS). However, to estimate OS accurately requires a sufficient number of patients to have died, which may take a long time. If an alternative endpoint is sufficiently highly correlated with OS, it can be used as a surrogate. Progression-free survival (PFS) is the surrogate most often used in oncology, but does not always satisfy the correlation conditions for surrogacy.We analyse the methodologies used when extrapolating from PFS to OS. Methods: A wide range of methods has been used to determine the appropriateness of surrogates.While usually adhering to reporting standards, the standard of scholarship appears sometimes to be questionable and the reporting of results often haphazard.
Conclusion:Standards of analysis and reporting PFS to OS surrogate studies should be improved by increasing the rigour of statistical reporting and by agreeing to a minimum set of reporting guidelines. Moreover, the use of IPD to assess surrogacy should increase.