Cancer clinical trials include research in four different phases. Each phase answers questions about the new treatment.

Phase I trials test new treatments for safety in humans and any harmful side effects. Within this phase, the safe dosage and determining how the new treatment should be given are examined. These studies usually include a limited number of patients who would not be helped by other known treatments. Typically this group consists of only 15-30 participants.

Phase II trials determine whether the new treatment is effective against specific tumors. A small number of people participate because risks and benefits are largely unknown. Typically this group consists of only 100 participants.

Phase III trials compare the result of people taking the new treatment with results of people taking standard treatment. Phase III testing occurs only when a protocol shows promise in Phases I and II. Typically this group consists of 100-thousands of participants.

Phase IV trials further determines the long-term safety and effectiveness of a new treatment. Typically this group consists of several hundred to several thousands of participants.