Phase I Clinical Trials

Clinical trials phases and design

Although less than 5% of patients with cancer are enrolled in clinical trials, such trials represent an important step between basic cancer research and clinical practice.1 Clinical trials serve as the basis for evidence-based medicine by addressing specific clinical questions, which may lead to improvements to current clinical practice.

The Various Phases of Clinical Development

Investigating the efficacy and safety of an agent or combination of agents through clinical trials involves multiple phases of development, beginning with smaller Phase I trials and culminating in large, randomized Phase III trials. Phase IV trials may also be conducted to gather additional information.2

Clinical trials by phase2

Trial phase Definition
Initial trial of a drug in humans for dosing, safety, and early efficacy information (20-80 patients*)
II Subsequent trial of a drug's safety and efficacy in a particular disease setting (100-300 patients*)
III Larger trial comparing a drug with best available therapy to confirm efficacy and safety; often used for drug approval (1, 000-3, 000 patients*)
IV Trial conducted after US Food and Drug Administration (FDA) approval to gain additional information about the drug's risks and benefits (thousands of patients*)

Design of clinical trials

When designing a clinical trial, it is important to define a number of parameters in order to generate meaningful results. These parameters include the patient population to be studied, treatment(s) to be investigated, endpoints, and how the trial will be conducted (eg, randomized vs nonrandomized).

The patient population

When selecting the patient population to be studied in a clinical trial, investigators should include patients who are likely to benefit from the intervention being tested.3 The population should also be selected such that the results of the trial can be generalized to patients in clinical practice. In general, the more diverse the patient population, the more generalizable the results may be to the wider patient population.4

In order to study a patient population of the appropriate disease state and level of diversity, investigators define inclusion and exclusion criteria that determine whether or not a patient is eligible for a trial. Inclusion and exclusion criteria can include patient characteristics (eg, age) as well as disease- and treatment-specific characteristics (eg, number and type of prior therapies).4

Use of controls in a clinical trial

In controlled trials—most Phase III and some Phase II trials fall into this category—the agent or regimen being investigated is compared to a control. The control may be either a placebo (if no effective therapies are available for the disease being studied) or a standard treatment—one in wide use and considered effective at the time the trial is designed.2 Although placebo is sometimes used as a control in clinical trials, it is rarely used in oncology trials where there may be ethical issues with this approach. It is important to note that because some clinical trials take months or even years to complete, the standard treatment may no longer be in wide use by the time results from the trial are reported.

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Popular Q&A

When Is IRB Review of Clinical Trial Websites Required?

When information posted on a clinical trial website goes beyond directory listings with basic descriptive information, such information is considered part of the informed consent process and therefore requires IRB review and approval. Basic descriptive information includes:

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