Phase 2 trials usually involve less than 100 people. The trials aim to see how well the new treatment works against cancer and to monitor for side effects. Phase 2 trials generally involve people who have already had cancer treatment. The chance of the treatment being tested in a Phase 2 trial being effective depends on the type and extent of the cancer and its response to previous treatment. If the new treatment shows promising effects (efficacy) against cancer and is safe then it is tested in Phase 3 trials.