I think they said on the call that they wanted to do the initial trials with discrete cohorts(not exact wording)-
My understanding was if they allowed too many variations within the cohorts, they may not be as likely to be able to determine anything definitive about the comparative efficacy of 113.
The other alternative, would be to expand the size of the study, which would probably take longer, defeating the purpose of an initial dose escalation study.
For all we know, they may have already added an arm including brain mets, but just didn't want to disclose because it may suggest proprietary information about the efficacy of the drug(which is what would cause them to add such) that they didn't for competitive reasons, want to disclose at this point.
