If the treatment seems to be a significant improvement over the standard treatment, that also is immediately shared. This random assignment process eliminates bias and ensures that an equal number of patients receive each treatment. The problem is that doctors might select therapies for their patients in a way that tends to invalidate the results of the study. For example, the youngest and healthiest patients might be chosen for the most aggressive and riskiest therapy. Then, if the therapy looks promising, it might be due to the fact that the patients who received it had a better original prognosis.
All patients receive the same investigational treatment.
This type of study is used when no one knows if any treatment will be effective, or if other factors might be affecting results, such as a method of delivery. There are very few placebo studies for brain tumors. And, no study uses a placebo without informing patients that they might receive one. In a double-blind study, neither the doctor nor the patient knows which drug is being given. In a single-blind study, the patients don't know which treatment they are receiving.