I wonder if you can help me understand the following comment I received on a study:

So, there are 3 patient groups (A, B and C):

Group A receives treatment X

Group B receives treatment Y

Group C received treatment Y followed by treatment Z.

Results (the numbers are made up):

Group B patients (n=50) have a median survival time of 36 months (range 11-49 months)

Group C patients (n= 31) have a median survival time of 43 months (range 21-69 months)

Statistical analyses showed that the median survival times of group B&C are not statistically different (P=0.06). Since they are not statistically significantly different, I want to combine groups B+C for further analyses. The feedback I received on that was: Since patients in group C only received treatment Z

*only if*they survived long enough to do so and the survival range in group B is lower than group C, I have to exclude all group B patients that survived less than 21 months (i.e. 11-21 months survival). Is this correct or can I refute this argument?

Thanks a lot and I hope this is not too basic

Jan