First you need to know what the signs of a treatment working are. If you cancer does not grow during a treatment then it is considered partially successful as it is preventing growth. I know that this is not really comforting as you what to get rid of the cancer, but if the current treatment is keeping it in check then waiting for a month using the current treatment is not a big deal.
When going into a trail you need to be fully informed as to how the trial is being run and whjat to expect. This means asking a lot of questi9ons. In trials either everyone is given the new drug or some are given the new drug and some are given the olf treatment and they don't tell you which you will get. If the old drug holds it at bay then thee isn;t much to loose but if it is growing on the old drug you want to maximize the chances of getting the new drug. You also need to know the risks that the new drug entails. Often it is difficult to know what the side effects will be going ibnto the trial and there may be real risks involved. Get all of the information you can before making a decision.
That being said trials can and do offer the hope of breakthrough results that may help you and iof the current treatment is not getting the results you want then they are deffinatly worth a go. If thing aren't working out then you can always drop out. You also usually get monitored much more closely during a trial and at reduced or no cost to you so that is a plus. Good Luck