Key Facts About Clinical Trials

  • Clinical trials are carefully designed research studies that test new treatments, drugs, or approaches to cancer care
  • Every FDA-approved cancer treatment available today was first tested in a clinical trial
  • Participants receive close medical monitoring and may gain access to promising new therapies before they are widely available
  • Only about 5% of adult cancer patients participate in clinical trials, yet these studies are essential for advancing cancer care

What Are Clinical Trials?

Clinical trials are scientific studies that evaluate whether new medical approaches work safely and effectively in people. In cancer research, clinical trials may test new drugs, drug combinations, surgical techniques, radiation methods, immunotherapies, screening tools, or supportive care strategies. Trials follow strict protocols approved by regulatory bodies and institutional review boards (IRBs) to protect participant safety.

Clinical trials are the only way to determine whether a promising treatment discovered in the laboratory actually helps patients. Without participants willing to enroll, progress against cancer would stop. Trials also help researchers understand which patients are most likely to benefit from specific treatments, moving toward more personalized cancer care.

Phases of Clinical Trials

Cancer clinical trials proceed through a series of phases, each with a distinct purpose and participant profile. A treatment must successfully complete each phase before moving to the next.

Clinical Trial Phases Diagram A diagram showing the four phases of clinical trials as a progression from Phase I testing safety in a small group, through Phase II testing efficacy, Phase III comparing to standard treatment in large groups, to Phase IV monitoring after FDA approval. Each phase shows the typical number of participants and primary goal. Phases of Cancer Clinical Trials Phase I Safety & dosing 15–30 patients Months–1 year ~70% proceed Phase II Efficacy testing 25–100 patients 1–2 years ~33% proceed Phase III Comparison trial 100–3,000+ patients 1–4 years ~25–30% approved Phase IV Post-approval 1,000s of patients Ongoing Long-term safety Is it safe? What dose? Does it work? Side effects? Better than standard care? Long-term effects? FDA Approval (if Phase III succeeds) The entire process from Phase I to FDA approval typically takes 6–12 years. Accelerated and breakthrough designations can shorten this timeline for promising therapies.
The four phases of cancer clinical trials, showing how treatments progress from initial safety testing to FDA approval. Each phase has increasing participant numbers and more rigorous evaluation criteria.

Phase I: Safety and Dosing

Phase I trials are the first time a new treatment is tested in humans. The primary goal is to determine a safe dose and identify side effects. These trials typically enroll 15 to 30 participants, often patients whose cancer has not responded to standard treatments. Participants receive increasing doses of the treatment (dose escalation) while researchers carefully monitor for adverse effects.

Phase II: Effectiveness

Once a safe dose is established, Phase II trials test whether the treatment actually works against a specific cancer type. These trials enroll 25 to 100 patients and measure outcomes such as tumor shrinkage, disease stabilization, and duration of response. Side effects continue to be closely tracked.

Phase III: Comparison

Phase III trials are large-scale studies that compare the new treatment to the current standard of care. Hundreds or thousands of patients are randomly assigned (randomized) to receive either the new treatment or the existing best treatment. These trials provide the strongest evidence of whether a new approach truly improves outcomes. Successful Phase III results are required for FDA approval.

Phase IV: Post-Approval Monitoring

After a drug receives FDA approval, Phase IV trials continue to monitor its long-term safety and effectiveness in a broader patient population. These studies may identify rare side effects not seen in earlier phases or explore new uses for the treatment.

How to Find Clinical Trials

  • ClinicalTrials.gov: The largest database of clinical trials worldwide, maintained by the National Library of Medicine. You can search by cancer type, location, and phase.
  • NCI Cancer Information Service: Call 1-800-4-CANCER or visit cancer.gov for personalized trial matching assistance
  • Your oncologist: Ask your cancer doctor about trials available at your treatment center or through research networks
  • Cancer center websites: NCI-designated cancer centers list their open trials online
  • Patient advocacy organizations: Groups like the Leukemia & Lymphoma Society, Lung Cancer Alliance, and others maintain trial-matching services for their specific cancer communities

Before enrolling in a clinical trial, you will go through the informed consent process. This is not just signing a form — it is an ongoing conversation with the research team to ensure you fully understand:

  • The purpose of the study and what treatment you will receive
  • Possible risks, side effects, and benefits
  • Alternative treatments available outside the trial
  • Your right to leave the trial at any time without affecting your standard care
  • How your privacy and medical information will be protected
  • What costs the trial covers and what you may be responsible for

Take your time reviewing the consent document. You may bring it home, discuss it with family, and ask questions before making a decision. You can also withdraw consent at any point during the trial.

Eligibility and Randomization

Each clinical trial has specific eligibility criteria that define who can participate. Common criteria include cancer type and stage, prior treatments received, age, overall health status (measured by performance status scales), organ function (kidney, liver, blood counts), and sometimes specific tumor biomarkers.

In randomized trials, participants are assigned to treatment groups by a computer-generated process — not by the patient or the doctor. This ensures fair comparison between groups. Some trials are “blinded,” meaning participants (and sometimes doctors) do not know which group they are in, to prevent bias in evaluating results.

Placebos in Cancer Trials

Many patients worry about receiving a placebo (“sugar pill”) instead of active treatment. In cancer clinical trials, placebos are rarely used alone. The ethical standard requires that all participants receive at least the current best available treatment. A trial might compare “standard treatment plus new drug” versus “standard treatment plus placebo,” ensuring no one goes without effective care.

Risks and Benefits

Potential Benefits Potential Risks
Access to new treatments before public availability New treatments may have unknown side effects
Close monitoring by a specialized research team The new treatment may not be more effective than standard care
Contributing to knowledge that helps future patients More frequent visits and tests may be required
Trial-related medical costs are often covered Travel and time commitments can be burdensome
Additional tests may detect other health issues early Insurance may not cover all non-trial costs

Questions to Ask Before Enrolling

  • What is the purpose of this trial and what phase is it?
  • What treatment will I receive, and how does it differ from my current options?
  • What are the known side effects and risks?
  • How long will the trial last, and how often will I need to visit?
  • Will my insurance cover the costs, and what expenses will the trial sponsor pay?
  • Can I continue seeing my own oncologist during the trial?
  • What happens if my cancer gets worse during the trial?
  • Will I be able to access the treatment after the trial ends if it works?
  • Is there a data safety monitoring board overseeing this trial?

Costs and Insurance

Under the Affordable Care Act, health insurance plans are required to cover routine patient care costs in clinical trials, including doctor visits, lab tests, and imaging that would be part of standard care. The trial sponsor (often a pharmaceutical company or the NCI) typically covers the cost of the experimental treatment itself, along with any extra tests required solely for the research.

Out-of-pocket costs may include transportation to the trial site, lodging if the site is far from home, and time away from work. Many organizations offer financial assistance for trial participants, including travel grants from the NCI, pharmaceutical companies, and patient advocacy groups. See our financial assistance guide for specific programs.

Myths vs. Facts

  • Myth: Clinical trials are a “last resort.” Fact: Trials are available at every stage of cancer, including newly diagnosed patients. Some of the best outcomes come from participating early.
  • Myth: I will definitely receive a placebo and no real treatment. Fact: Cancer trials almost always provide at least the standard of care to every participant.
  • Myth: I will be treated like a “guinea pig.” Fact: Trials have extensive safety oversight, including IRBs, data safety monitoring boards, and federal regulations.
  • Myth: My insurance won’t cover anything. Fact: Federal law requires insurers to cover routine care costs in qualifying clinical trials.
  • Myth: I can’t leave a trial once I start. Fact: You can withdraw at any time, for any reason, without penalty to your ongoing care.

Be Cautious of Unverified Trial Claims

Be wary of websites or individuals claiming to offer “miracle” cancer treatments through unofficial trials. Legitimate clinical trials are registered on ClinicalTrials.gov, conducted at established medical institutions, reviewed by IRBs, and never require participants to pay for experimental treatments. If something sounds too good to be true, verify it with your oncologist or the NCI.

Related Resources

Last reviewed: March 2026. Clinical trial availability changes frequently. Always consult your oncologist and check ClinicalTrials.gov for the most current trial listings relevant to your cancer type and situation.