No, they can't. To do so would introduce confounding variables in the inevitably unique way they treat their subjects, even if it's just knowing you're part of

No, they can't. To do so would introduce confounding variables in the inevitably unique way they treat their subjects, even if it's just knowing you're part of the experiments. For maximum assurance of conclusions, such studies need to be double-blind: neither the subjects nor the researches who interact with them are to know who's taking just chemo and who's taking the new treatment.