FDA Staff Concern on Overall Survival Data: Historically, FDA staff has advised/raised concerns about overall survival and acceptance/approval of drugs. For example, in March 2023, the FDA staff also highlighted Polivy’s, a drug treating DLBCL, and its lack of an overall survival benefit. 
At the FDA's request, Roche previously postponed its application to wait for longer follow-up data. But after a median follow-up of nearly 40 months, the death risk reduction was still low at 6%, according to an update at the American Society of Hematology annual meeting in December 2023. https://www.fiercepharma.com/pharma/what-practice-changing-polivy-fda-challenges-roche-drug-ahead-lymphoma-expert-hearing

However, the passage of the drug prevailed as medical professionals got to vote. Roche filed against FDA staff recommendation, got 11 to 2 vote from the Oncology Drug Advisory Board and received FDA approval for their drug.  
https://www.fiercepharma.com/pharma/fda-advisers-backs-roches-blockbuster-polivy-dream-front-line-lymphoma 

October 2023, Novartis CEO. “We’re a little bit in new territory,” Narasimhan said, “insofar as the FDA, I think, has made a significant shift affecting all cancer drugs with respect to the expectations of OS at the filing with PFS.”

The FDA also encourages patient-friendly cancer studies in which crossover from the control arm onto the experimental therapy is allowed. Companies are now in a bit of a “conundrum” trying to manage that because the FDA doesn’t like crossover-adjusted overall survival analysis, Narasimhan said.
https://www.fiercepharma.com/pharma/novartis-emerges-sandoz-spinoff-strong-sales-delays-pluvicto-fda-filing