Clinical Trials


A clinical trial is a research study used to evaluate the safety and effectiveness of new treatments. When cancer patients have exhausted all established therapies, they often try to find a relevant clinical trial.

Clinical trials are divided into four phases, Phase I, Phase II, Phase III and Phase IV.

  • The purpose of a phase I trial is to determine safety. It involves a small number of individuals, typically 20-80. Often it involves healthy volunteers, although sometimes they also try it on patients who volunteer. Phase I trials evaluate dose-dependent side effects of a treatment, including toxicity.

  • The purpose of a phase II trial is to determine effective dosing levels and short-term efficacy of a treatment for a particular indication. The phase II trial also confirms safety and monitors for side effects. It involves a larger number of individuals, typically 100-300.

  • The purpose of a phase III trial is to compare effectiveness with existing therapy in a scientifically well-founded manner (double-blind randomized between the two arms of the study) and over a longer period of time. It involves a large number of patients (usually more than 500).

  • Phase IV trials are conducted after a treatment has been approved. Usually they are used to evaluate the long-term safety and effectiveness.

Usually one starts hearing about a new "wonder drug" toward the end of its phase II trials. However, one should not reach conclusions based on phase II trials, as promising results have a tendency to evaporate once the therapy is submitted to the rigor of a phase III trial.

In essence, a phase II trial demonstrates whether a new drug shows promise and identifies the appropriate treatment level, and a phase III trial confirms whether or not that promise is real. Until the phase III trial is complete, the new drug should be considered experimental.

One should not pursue the therapy being tested in a clinical trial unless one is participating in the trial and fully understands the risks. There is a great tendency to want to try a therapy that fared well in a phase II trial. But until that therapy has completed phase III trials, it is unproven.

To find out about new clinical trials for cancer patients, visit the National Cancer Institute's Cancer Clinical Trials site or A resource for patients in the Mid-Atlantic with bladder, kidney and prostate cancer is GUMDROP Trials (1-888-808-7414).

Copyright © 2005-2018 by Mark Kantrowitz. All rights reserved.

Suggestions and corrections are welcome and should be sent to .