For this type of reaction they will need to be damned sure of the data so that is why I think we will hear something regarding it no earlier than the end of the 2nd cohort group first cycle completion.  They will then have had 2 cycles of the 1st cohort and 1cycle of the 2nd cohort for blood tests and that should be plenty enough to confirm the p53 activation and they may even wait to do the p21 tests after the 2nd cohort 1st cycle to lump the total data into a monstrous PR event such as you envision.  IMO.