Agreed. You only want to measure one variable at a time.

Think about this: what if Bril-OM doesn't work as well when the tissues have already been damaged by a round of chemo and/or radiation? You wouldn't be able to tell what the true efficacy of Bril-OM was.

I could see having a second arm opened up, where you deliberately tried it on people who had already had oral mucositis problems from previous treatments -- but first we need to know whether it works, before going to the expense of an additional trial arm.