RE:RE:eyes on the prizeIn general, the association between ORR and PFS, and that between PFS and OS, are stronger than the association between ORR and OS, which may indicate a pass-on effect of ORR to PFS to OS.
The fine surrogacy of ORR for PFS to some extent comes from the definition of those two indices. Notably, it seems that ORR works better as surrogacy for PFS in both immunotherapy and targeted therapy than that in chemotherapy.