Phases of Clinical Trials

Cancer clinical trials involve a series of steps, called phases. If a new treatment is successful in one phase, it moves on to the next.

During the early phases (phases I and II), researchers find out if a new treatment is safe, what – if any – side effects the treatment has, the best dose, and if it has some benefit for the patient. Phase III looks at whether the treatment is better than other treatments already available. Phase III also includes large numbers of patients to make sure the results are valid.

Phase I

Number of patients: 15 to 30 (learn more about Phase I trials)

  • Determine a safe dose
  • Decide how the new treatment should be given
  • See how the new treatment affects the human body

Phase II

Number of patients: Less than 100

  • Determine if the new treatment has an effect on a certain cancer
  • See how the new treatment affects the body

Phase III

Number of patients: from 100 to several thousand

  • Compare new treatment with current treatments

Phase IV

  • Study the long-term effects of treatments already approved by the FDA

Some researchers combine two phases (phase I and II or phase II and III) in a single protocol. This type of combined clinical trial may allow questions to be answered more quickly or with fewer patients.