Can I switch groups if mine is not working?

Usually not, because switching would destroy the comparison the whole trial depends on. But some trials are built with crossover, where you can move to the other treatment at a set point.

Ask before you join whether crossover is allowed, and what happens if your cancer grows during the trial. That answer should be in the protocol already.

Written by two physicians. Checked against patient information from the US National Cancer Institute and Cancer Research UK.