I could be completely off base, but my impression

I could be completely off base, but my impression is that the FDA requirements for large groups of patients, and long term trials is more for the safety than for the efficacy. Based on some drugs that have been approved with poor efficacy.

So, I think given that we have 5 years and 800+ patients to demonstrate the safety, we have an advantage in that we really just need to show efficacy.

Others have stated that the FDA views cancer efficacy through the lense of extending survival, by as little as 2 months.

So, I would think with our impressive safety profile, if we show that we are extending life we have a good chance at BTD approval. The big question is how many patients will we need?