In a RCT we would like to compare oncological outcome of two surgical 2-stage strategies, i.e. patients require to undergo both stages to become free of cancer. The problem is that strategy A generally takes less time to come to the second stage becoming free of cancer. On the other hand, in strategy B some patients might not even get to the second stage of their therapy because of the longer time between stage 1 and 2, i.e. in this longer interval they run the risk of disease progression or not getting fit for stage 2.
My question is, from which time-point should our overall survival be calculated? Starting at randomisation or starting at completion of stage 2. We believe at randomisation.
Should the starting point be different for recurrence-free OR progression-free survival?
Is it at all possible to compare recurrence-free survival between the two groups as some patients in strategy B might not proceed to their second stage (and become free of disease at all, which is a requirement for being able to assess the event 'recurrence')?