Key takeaways
Exploring different treatment options for cancer can be one way to take an active role in your care. For some people, clinical trials may offer access to new approaches to treatment that are still being studied.
Understanding how trials work, what participation involves, and how participants are protected can help you decide whether participating in a clinical trial is something to discuss with your care team.
What are cancer clinical trials?
Cancer clinical trials are research studies that help doctors and researchers learn more about cancer and how to prevent, detect, diagnose, or treat it. These trials may study new treatments (such as drugs, devices, or procedures), new tests for detecting or diagnosing cancer, or different ways of delivering care.
To protect the rights and safety of participants, cancer clinical trials follow strict plans, are reviewed by independent ethics committees, and include layers of oversight. The goal of clinical trials is to better understand how new approaches to cancer care work, including how they affect the body and what side effects may occur. This research helps build evidence to guide future care.
Your care team might mention trials at different points in cancer care, depending on what researchers are trying to learn from the trial. Trials exist across different types of cancer, stages, and treatment goals.
Being told about a trial does not mean you have to join. Participation is always optional, and you can talk with your healthcare team about what a specific trial would involve. Choosing not to join a trial will not affect the level of care your team provides.
Clinical trial phases and how they work
Clinical trial phases help explain what a trial is trying to learn at a particular point in the research process.
Each phase of a trial—Phase 1, Phase 2, Phase 3, and Phase 4—gives a general sense of the trial’s focus. This includes early questions about safety and dosage and later questions about how well an approach works, how it compares with current care, or how it is monitored after approval.
- Phase 1: Focuses on safety and dosage, typically involving smaller groups.
- Phase 2: Explores effectiveness and side effects.
- Phase 3: Compares approaches in larger populations to understand effectiveness and safety.
- Phase 4: Focuses on longer-term monitoring.
Not all studies reach every phase. Some studies may stop early if researchers do not get the information they need to continue.
In many cancer clinical trials, treatments are tested against a control group, which is the group researchers use as a point of comparison. The control group usually receives a standard cancer treatment already in use. In cancer trials, placebos are generally not used in place of effective standard treatment when one is available.
Here is what the phases of clinical trials generally mean:
Clinical trial phase 1: Safety and dosage
- Phase 1 trials are usually the first time an investigational treatment or approach is studied in people.
- These trials generally have a smaller number of people participating. In oncology, they are typically conducted in patients with cancer (not healthy volunteers) due to the safety profile of treatments.
- The focus of these trials is on understanding safety, dosing, and how the body processes the treatment under investigation.
- Researchers test for side effects and identify a dose that appears to be both safe and effective enough to test further.
Clinical trial phase 2: Effectiveness and side effects
- Phase 2 trials usually include more people than Phase 1 trials. In cancer clinical trials, phase 2 is designed to learn more about how a treatment or approach works in people with a specific type or stage of cancer.
- At this stage, researchers begin to look for signs that the treatment may be having the intended effect. For example, they may assess whether cancer responds to treatment, whether symptoms or test results change, or whether the approach affects the body in the way researchers expected.
- Researchers continue to closely monitor side effects, including how often they occur, how severe they are, and whether any new safety concerns appear as more people receive the treatment.
Clinical trial phase 3: Effectiveness and safety (larger populations)
- Phase 3 trials are for treatments that have passed phases 1 and 2.
- They typically include larger populations, and researchers compare different approaches to better understand safety and effectiveness in broader groups. Phase 3 trials are often used to support regulatory approval.
- These trials may take place over longer periods of time so researchers can collect enough information about how well the treatment works and what side effects may appear.
- In many Phase 3 trials, participants are assigned to groups by chance (randomization). One group may receive the treatment being studied, while another group may receive the current standard treatment, another comparison approach, or, in some cases, a placebo.
- When an effective standard treatment is available, placebos are generally not used in the place of that treatment.
Clinical trial phase 4: Long-term monitoring
- Phase 4 trials happen after a treatment has been approved and is available for use.
- They are not required for every treatment option.
- These trials focus on continued data collection, such as long-term safety monitoring or how an approach is used in real-world clinical settings.
Protecting participant safety
Clinical trials include multiple layers of oversight and are designed to help protect participant rights, safety, and well-being. Several safeguards are in place to help protect participants throughout a clinical trial.
Independent Institutional Review Boards (IRBs): These are also known as ethics committees. They review clinical trial protocols before a trial begins and continue oversight while the trial is going on. Their role is to help ensure that participant rights, safety, and well-being are protected.
Informed consent: If you are considering taking part in a clinical trial, you will go through a process called informed consent. This means you will be given information about the trial so you can make an independent decision about whether to participate, including:
- The purpose of the trial.
- What taking part in the trial involves, such as trial visits, tests or scans, treatments, questionnaires, follow-up appointments, and timing.
- Possible risks, potential benefits, and alternatives.
- Any costs that could result from joining.
Additionally, many cancer treatment trials compare a new approach with the current standard treatment rather than withholding care. If a trial uses a placebo, that information should be explained up front in the consent materials.
You will have time to ask questions and decide what is right for you. You can also continue to ask questions throughout the trial. Even after you sign consent paperwork, you always have the right to leave a clinical trial at any time, for any reason.
Ongoing safety monitoring: Clinical trials are monitored for safety throughout the trial. Side effects and other safety information are collected and reviewed, and trials may be modified or stopped if concerns arise.
Regulatory oversight: In the United States, the Food and Drug Administration (FDA) plays a role in overseeing clinical trials and ensuring that regulatory requirements are met.
What to expect if you join a clinical trial
Every trial is different, but many studies have similar themes.
Screening and eligibility: Most trials have eligibility criteria. These requirements help ensure the trial is comprised of people who fit the research focus. You may hear terms like inclusion criteria (i.e., what you need in order to participate) and exclusion criteria (i.e., what could prevent someone from joining).
Before joining a trial, you may undergo screening to determine whether you are able to take part. Screening may involve reviewing your medical history and doing tests to confirm whether the trial is a match.
Trial visits and procedures: If eligible and interested, you may attend scheduled visits, undergo tests or assessments, and talk with the team throughout the trial. The level of participation and time commitment can vary depending on the trial design.
Communication with the trial team: You will usually have a point of contact, such as a trial coordinator or research nurse, who can help with logistics and questions.
Costs and insurance coverage: Costs associated with clinical trials can differ based on the trial and individual circumstances. Research costs may be covered by the trial sponsor, but out-of-pocket costs (like parking or childcare during the trial) will depend on the trial. Costs for routine medical care (like lab tests or clinic visits) may also be billed to you or your insurance depending on the trial. These details are typically discussed with the healthcare team or trial staff before you decide to join, and they can help clarify what may be covered and what questions to ask.
How to find and explore clinical trials
If you are interested in learning whether a clinical trial may be an option for you, your oncology team is the best place to start. They can help you understand whether any trials may be relevant to your cancer type, stage, treatment history, and overall care plan.
Public trial databases can also be useful for seeing what studies are available, but trial listings can include technical language and eligibility criteria that can be difficult to interpret without medical context. Your healthcare provider can help explain what a specific trial may involve and whether it could be appropriate to participate.
Start with your oncology team. You can ask if there are trials that might fit your diagnosis and treatment history, what participation could involve, and what the potential pros and cons may be in your situation.
Search publicly available databases, such as the federal registry ClinicalTrials.gov, which list clinical trials happening in the United States and internationally. Some organizations also maintain their own trial listings, such as PfizerClinicalTrials.com. These listings provide information about the trial’s purpose, eligibility criteria, locations, and who to contact.
Bring what you find back to your clinician. Even if a trial looks like a match online, only a qualified clinician and the trial team can confirm whether it fits your medical situation. The most helpful next step is usually to bring the trial name or National Clinical Trial (NCT) number to your next appointment and ask what it could mean for you.
Bring your questions to your next doctor's visit
Cancer clinical trials are one way that researchers study new approaches to cancer care, and each trial is designed to answer specific questions about safety, effectiveness, side effects, or longer-term monitoring.
Knowledge of how trials are structured, what the different phases mean, how participant rights and safety are protected, and what taking part may involve can help you prepare for conversations with your healthcare provider.
As a next step, Prepare for Care by writing down your questions and reviewing them with your care team. For additional information about clinical trials, you can visit PfizerClinicalTrials.com.
Frequently
asked questions
Are clinical trials safe?
Clinical trials are highly regulated and incorporate strict safety protocols, but no medical research is completely without risk.
Trials are reviewed before they begin by an independent ethics committee, and safety is monitored throughout the trial. Participants are also given information through informed consent, including what the trial involves, possible risks and potential benefits, and their right to leave at any time. Researchers review side effects and other safety findings during the trial, and a trial may be changed or stopped if concerns arise. In the United States, the FDA plays a role in overseeing clinical trials and protections in place for participants.
What is informed consent?
Informed consent is the process of giving you information you would reasonably want to know before deciding whether to join a trial. This includes details about the purpose of the trial, what participation involves, and possible risks. You will have the opportunity to ask questions and take time to decide.
Informed consent is ongoing, meaning you can continue to ask questions throughout the trial, and you have the right to leave the trial at any time.
Can I leave a trial after joining?
Yes, you can leave a trial after joining. Participation in clinical trials is voluntary, and you can stop at any time.
Will I get a placebo?
Placebos used on their own are rare in cancer clinical trials. In modern cancer trials, even the patients in the placebo group almost always receive standard treatment in addition to the placebo, meaning you may still be treated for cancer if treatments are available. If a placebo is used, you should be told ahead of time, and the details should be included in the consent information. A placebo used alone, without standard treatment, generally happens only when no standard treatment is available.
What is randomization in a clinical trial?
Randomization is a process used in some clinical trials to assign participants to different groups by chance. This helps researchers compare approaches in a fair and unbiased way. In randomized trials, you cannot choose or know in advance which group you are in. Your healthcare team can explain whether randomization is part of a specific trial.
Do clinical trials cost money to join?
Costs and insurance coverage can vary depending on the trial and individual circumstances. Some parts of a trial may be covered by the trial sponsor, while others may be billed to you or your insurance. These details are typically discussed with your healthcare team or the trial staff before you decide to take part.
Cancer resources and guidance
Discover information to help you understand cancer and talk to your doctor.
- /cancer/education/systemic-cancer-treatment-types
- /cancer/education/when-to-get-biomarker-testing
- /cancer/education/cancer-biomarkers
- /cancer/education/cancer-tests
References
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Fred Hutchinson Cancer Center. Health insurance and clinical trials. Updated June 1, 2026. Accessed July 7, 2026. https://www.fredhutch.org/en/research/clinical-trials/guide-clinical-trials/health-insurance.html.
National Cancer Institute. Clinical Trial Facts. Updated January 3, 2025. Accessed June 8, 2026. https://www.cancer.gov/research/participate/clinical-trials/facts.
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