Understanding Gynecologic Oncology Group (GOG) Clinical Trials

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Phases of GOG studies

In general, Phase I studies determine safety of a new treatment, Phase II studies determine efficacy and Phase III studies determine superiority.


Phase I studies involve new treatments whose effects in humans are largely unknown. This phase is used to determine how to use the new treatment in a safe manner to the best effect.

Candidates for Phase I studies are usually individuals with cancers beyond cure, but without localized growths that can be measured.

Often a Phase I study tries to determine safe doses for a new treatment. The study begins with a low dose which is increased until side effects are encountered.


Phase II studies are investigations to determine if a particular treatment whose safety has been established has merit in treating a particular cancer. These treatments are usually new, or they may be an application of a old drug in a new setting.

When a Phase II study has shown that a significant effect has been achieved with a treatment, then that treatment becomes a candidate for inclusion into a Phase III study.

Typically, candidates for Phase II studies are individuals with cancers that have resised the standard treatment, and which have a mass that can be measured on an X-ray, scan, or by examination. This allows effects of the treatment to be measured and timed.


Phase III involves randomized studies in which the entire group particates. Participants with similar types of cancer are assigned to one of two or three treatment regimens. Typically, one treatment is the standard approach and the others are the new rivals. Assignments must be random to ensure reliable,unbiased results. No scientifically meritorious study can be accomplished any other way.

It is important to understand that each treatment option in the study is considered by members of the G.O.G. to be effective and up-to-date. It is unlikely that women who participate in any of the treatment regimens will be ill served. Phase III studies compare how likely a treatment is to work, how long the effects last, the short and long term side effects, the costs, etc., and determine which treatment is better overall.

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