[Correspondence] Lessons learned from the BOSS trial

We welcome the discussion of the BOSS trial1 by Rebecca C Fitzgerald and Peter Sasieni.2 Interpretation of these data is important to inform future guidelines. The authors suggest that using all-cause mortality as our primary endpoint was a mistake. The choice of outcome measure for cancer screening programmes has been debated and there are strong arguments for using all-cause mortality as a hard endpoint, free from bias of attributing cause of death, particularly when trial allocation cannot be masked.