Exactly SkyLimit2022!!
That is exactly what I have tried to explain to our friend HyGro for a while now. PFS is used as a substitute for OS because OS can take a really long time to acquire the data. It is used to accelerate trials and presumed to be a surrogate measure but in most cases the sponsor is obliged to do a follow-up study to prove that the assumption, that PFS is a good surrogate or proxy for survival is proven.
Unfortunately, besides pseudoprogression, there is also pseudoresponse and apparent delayed recurrence or improvement in PFS is frequently not correlated with improvement in survival, as has been the case with Keytruda and Opdivo in a number of cases. That is why the FDA last year reviewed some previous accelerated approvals again and withdrew some approvals, for this very reason. And despite not being correlated in some cases, they let some approvals remain, though the real benefit may still be in question.
In a case like this, where the trial was allowed to run for many, many years, and survival data is actually available, the real and concrete measure of survival, instead of a surrogate measure of benefit, can be provided. Beating hearts are an undeniable benefit and extremely positive. Add to that it is an orphan disease, typically 100% fatal and that the treatment has little to no side effects, and you have a compelling story for regulators to tell.
No one else is getting such results and while shorts can claim that it is due to some other factors, that hypothesis is not apparently in any other data and is without substance. The only explanation is the one that is proven, with significant statistical evidence, via this trial.
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