Following on from our blog post on the general introduction to clinical trials, today we will look at the different phases of clinical trials.

There are several different phases of clinical trials, and it is important to know what is involved in each phase as this will help you to determine if a trial is appropriate for you.  

Phases of clinical trials

The main phases of clinical trials are Phases 1, 2 and 3. These are sometimes referred to in Roman numerals I, II, and III.  In some instances, there can also be sub-phases, for example, Phase 3a and Phase 3b.  Just to add to the complexity, occasionally there is also a Phase 0 and Phase 4. So what do all these different phases mean to you as you think about enrolling?

Phase 0 is different from the other phases of trials as there is no benefit to the volunteer taking part; a Phase 0 trial is of benefit only to people in the future. Phase 0 trials use only a few small doses of treatment on only a few patients (typically fewer than fifteen people) and then look at how the body responds. Because doses are low, there is less risk in Phase 0 than in Phase 1. Phase 0 trials are not widely conducted.

Phase 1 clinical trials

  • The goal of Phase 1 clinical trials is safety evaluation. The trials look at what dose level can be safely given, how often and for how long (frequency and duration), without serious side effects/toxicity. Phase 1 trials are not designed to see if the treatment works against cancer.
  • This Phase is often the first time the treatment has been tested in people.
  • A small number of patients are enrolled (20+).
  • Placebos and control groups are not included.
  • This phase may include people with different types of cancer.
  • Often, patients must stay in the hospital for short periods of time to be carefully monitored.
  • Enrollment might be reserved for those patients for whom other attempted treatment options have failed.

Phase 1 trials have the most potential risk, because they represent the first time that the treatment has been used in people; however, they can help patients. As with all phases, but particularly Phase 1, careful consideration of the pros and cons is key before enrolling.

Phase 2 clinical trials

  • If a treatment is found to be reasonably safe in Phase 1 trials, it can then be tested in Phase 2 trials.
  • The goal is to determine if the treatment works.
  • The type of response investigated varies with each study. Possibilities include: shrinking the cancer; halting the growth of the cancer; delaying recurrence; improving quality of life; extending life.
  • Usually these trials involve 25-300 patients, all with the same type of cancer.
  • Generally all patients get the same dose, but occasionally different groups might test different dose levels/frequency.
  • No placebo groups are included.

Because more patients are enrolled, less-common side effects tend to show up in Phase 2 trials.

The FDA states that 30% of drugs tested in Phase 2 proceed onto Phase 3 testing.

Phase 3 clinical trials

  • If enough patients benefit from the treatment in Phase 2 trials and the side effects aren’t too bad, the treatment proceeds to a Phase 3 trial.
  • The goal is to compare the safety and effectiveness of the new treatment against the standard current treatment for a particular type of cancer.
  • Large numbers of patients – typically several hundred – are enrolled.
  • Phase 3 trials are often conducted in several different locations at the same time (within the country or internationally).
  • It is unusual for placebos to be used, but the test treatment is compared to another current standard treatment.
  • The studies are generally randomized, which means that when the patient enters a trial, they won’t know which treatment they will get. Where possible, the trials are “double-blind” – meaning that neither the patient nor the doctor knows which treatment the patient is getting. 

You might also see Phase 3 trials listed as 3a and 3b. Phase 3b trials tend to provide supplemental information to Phase 3. Phase 3b trials tend to be conducted after documentation of the effectiveness of the treatment has been submitted to regulatory authorities for approval, but before it is accepted and launched.

Phase 4 trials are conducted after the treatment has been approved by the regulatory authority. The goal of Phase 4 trials is to answer specific questions, such as cost effectiveness. You can get the same treatment without being part of a clinical trial but by enrolling in a Phase 4 trial, you help researchers find more information and as a result, your participation also helps future patients.

As you can see, as a treatment progresses through the different phases, the phase number gives you an indication of how many people have previously been tested. By enrolling in a phase 3 trial, you already know that this treatment has been given to several hundred people and seems to be having an effect, whereas if you joined a phase 1 trial you could be one of the first to try the treatment. 

As the phases progress, the length of the trial increases. Phase 1 trials are usually the shortest and only pick up short term effects, whereas as Phase 3 trials might last years and can provide long term data.

Knowing this information can help you make decisions based on the risk:benefit ratio and your particular situation.  

In the next few blog posts we’ll look more at the risk:benefit ratio, as well as the other things you should consider, and how to find clinical trials.

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