What Are Clinical Trials?
A plain-language explanation of what cancer clinical trials are, why they matter, and the main types, based on National Cancer Institute resources.
Source: National Cancer Institute · NCI reviewed 2024-11-03 · Verified 2026-07-02
5 min readBeginnerUpdated 2026-07-02
The 30-second version
Clinical trials are research studies that test how well new medical approaches work in people. In cancer, they test new ways to find, prevent, and treat cancer, and to improve quality of life. People join for many reasons, and past trials are a big reason people with cancer are living longer today.
Key takeaways
- Clinical trials are research studies that test how well new medical approaches work in people.
- Cancer trials test new ways to find, prevent, and treat cancer and to manage side effects.
- Past clinical trials are a reason people are living longer today.
- There are several types of trials: treatment, prevention, screening, and supportive/palliative care.
- People join trials for many reasons, including helping future patients.
The simple version
Clinical trials are research studies that test how well new medical approaches work in people. In cancer research, clinical trials test new ways to find, prevent, and treat cancer. They also help doctors improve the quality of life for people with cancer by testing ways to manage the side effects of cancer and its treatment.
In short: a clinical trial is a carefully run study that tests a new medical idea in people.
Why clinical trials matter
Today, people are living longer lives thanks to the results of past cancer clinical trials. When you take part in a clinical trial, you add to our knowledge about cancer and help improve cancer care for people in the future.
People join clinical trials for many reasons:
- People living with cancer often join because they want to help future patients.
- People with certain risk factors want to help doctors learn how to prevent cancer.
- Healthy volunteers want to help doctors learn how to find cancer early.
People with cancer and healthy volunteers join trials to play a role in cancer research and move science forward to help others.
The main types of trials
There are several types of cancer clinical trials. Each type is designed to answer different research questions.
- Treatment trials. Most cancer clinical trials are treatment studies that involve people who have cancer. These trials test new treatments or new ways of using existing treatments.
- Prevention trials. These look at ways to prevent cancer. In most prevention trials, the people who take part do not have cancer but are at high risk of developing it, or they have had cancer and are at high risk of a new cancer.
- Screening trials. The goal is to test ways to find cancer before it causes symptoms, when it may be easier to treat.
- Supportive care / palliative care trials. These look at ways to improve the quality of life of people with cancer, especially those who have side effects from cancer and its treatment.
In short: different kinds of trials answer different questions, from prevention to treatment to comfort and quality of life.
Learning more
If you are interested in clinical trials, your healthcare team can help you understand your options and where to look. Every trial is different, so it helps to ask questions and take your time.
Words to know
- Clinical trial
- A research study that tests how well new medical approaches work in people.
- Treatment trial
- A clinical trial that tests new treatments or new ways of using existing treatments in people who have cancer.
- Prevention trial
- A clinical trial that looks at ways to prevent cancer, often in people at high risk.
- Screening trial
- A clinical trial that tests ways to find cancer before it causes symptoms.
- Supportive care trial
- A clinical trial that looks at ways to improve the quality of life of people with cancer, especially side effects.
Frequently asked questions
▸What is a clinical trial?
Clinical trials are research studies that test how well new medical approaches work in people. In cancer research, they test new ways to find, prevent, and treat cancer. They also help doctors improve quality of life by testing ways to manage the side effects of cancer and its treatment.
▸Why are clinical trials important?
Today, people are living longer lives thanks to the results of past cancer clinical trials. When you take part in a trial, you add to what is known about cancer and help improve cancer care for people in the future.
▸Why do people join clinical trials?
People join for many reasons. People living with cancer often join because they want to help future patients. People with certain risk factors want to help doctors learn how to prevent cancer. Healthy volunteers want to help doctors learn how to find cancer early. All of them help move science forward to help others.
▸What are the main types of cancer clinical trials?
There are several types. Treatment trials test new treatments or new ways of using existing ones. Prevention trials look at ways to prevent cancer. Screening trials test ways to find cancer before it causes symptoms. Supportive or palliative care trials look at ways to improve quality of life for people with cancer.
▸Do you need to have cancer to join a clinical trial?
Not always. Most cancer trials are treatment studies that involve people who have cancer. But prevention trials often involve people who do not have cancer but are at high risk, and screening trials may involve healthy volunteers.
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Questions to ask your healthcare team
Consider bringing these questions to your next appointment.
- Is there a clinical trial that might be right for me?
- What type of trial would it be — treatment, prevention, screening, or supportive care?
- What is the purpose of this trial?
- How could taking part help me or help others?
- Where can I look for trials that fit my situation?
- Who can answer my questions about joining a trial?
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