Understanding Cancer Research Study Design and How to Evaluate Results

Aprobado por la Junta Editorial de Cancer.Net, 07/2022

Cancer research studies look for and find better ways to prevent, diagnose, and treat cancer. Doctors and scientists can design these studies in many ways to answer the questions they have. No study design is perfect. Each has strengths and limits.

When you are researching information about your or your loved one's cancer, it is important to understand how studies are designed. This can help you figure out what the results mean to you. Some research is very preliminary or "early", which means it will be a long time before the results affect patient care. Other research results may have an immediate impact on how doctors care and treat people with cancer.

There are 3 main types of cancer research studies:

Preclinical studies. This type of study is used in a laboratory to test whether a change in approach, called an intervention, may be useful to treat a cancer, and whether it appears to be safe. These studies are often done in cancer cells either in a petri dish or in an animal like a mouse. These results are very important for deciding which interventions to eventually test in people. Often, a lot of time will go by between testing interventions in the laboratory and having them available to treat people with cancer.

Experimental studies, called clinical trials. This type of study gives a group of volunteers an intervention. The intervention is the focus of the study. For instance, it may be a new treatment, medical device, or process. Researchers often compare the results of the intervention group to a group that does not get the intervention. This is known as the control group. For many studies, who does and does not get the intervention is selected at random, called randomization. In other studies, every person gets the intervention. Finally, there are some studies that use a specific selection process to make decisions about treatment.

Experimental studies and clinical trials help researchers learn more about how cancer starts or spreads. These studies can also test new imaging methods and ways to improve quality of life. Learn more about clinical trials.

Observational studies. This type of study observes groups of people in a natural setting. Researchers do not give an intervention. Instead they study the results of interventions already in place. For instance, researchers may find out whether a group of people has more cancer diagnoses than another group.

Observational research helps with the study of epidemiology. Epidemiology looks at how different risks influence, cause, or spread a disease in a community.

What are the types of experimental cancer research studies?

Experimental studies are more reliable than observational studies. This is because people in these studies are placed in the intervention group or control group, usually at random. Randomization lowers the chance that what they or the researchers assume or prefer will change the study results. These assumptions or preferences are called bias.

This type of study also helps researchers to better find and control for such features as age, sex, and other factors that can affect the results of the study.

Researchers may create specific rules, called eligibility criteria, when they ask people to join an experimental study. This often includes the type of cancer and the stage of cancer. This is to make sure the study's participants have specific things in common so the results are helpful for similar patients in the future.

Clinical trials and experimental studies test:

  • The effectiveness or safety of a new drug or combination of drugs

  • A new way of giving a kind of treatment, such as radiation therapy or surgery

  • A new treatment or way to prevent cancer

  • A new way to lower the risk of cancer coming back, called recurrence

  • A new way to relieve a side effect of cancer or its treatment

Researchers do clinical trials in segments called phases. Each phase of a clinical trial gives different answers about the intervention being tested. There are 4 phases of clinical trials.

In a phase 3 clinical trial, people in the study are usually randomly placed in either the intervention group or control group. Researchers can prevent bias in a clinical trial by keeping those people and themselves, or just those people, from knowing who is in each group. This is a process called "blinding."

The types of experimental studies include:

Double-blind randomized trial. The people in the study and the researchers do not know who belongs to the intervention group or control group. They find out only when the study ends. Most researchers feel this type of clinical trial produces the best study data.

Single-blind randomized trial. The people in the study do not know whether they belong to the intervention group or control group, but the researchers know.

Open or unblinded trial. The people in the study and the researchers know who belongs to each test group. This approach is used when it is not possible to use blinding. For instance, the study may be comparing a surgical treatment to a drug.

What are the types of observational cancer research studies?

In observational studies, researchers have less control over the people in the study. This means that certain factors could affect the results. However, these studies provide data that can help guide future research.

Types of observational studies include:

Case-control studies. These studies compare 2 groups of people. For instance, researchers could compare information about people with cancer and those who do not have cancer. People who have cancer are the case group. People who do not have cancer are then the control group. Researchers may look for lifestyle or genetic differences between the groups. By doing this, they hope to find out why one group has a disease and the other group does not. These studies are called retrospective. That means researchers study an event that has already occurred.

Cohort studies. These studies are prospective. That means researchers study an event as it occurs. They watch a group of volunteers for a long period of time and track something. For instance, they could track any new cancer diagnoses. This type of study can look at whether certain nutrients, exercise, or other action can prevent cancer. This approach can also find cancer risk factors. For instance, cohort studies have looked at whether postmenopausal hormone replacement therapy increases the risk of breast cancer.

Case reports and case series. Case reports are detailed reports of one person's medical history. If many people receive a similar treatment, the reports may be grouped into a case series. The results of case series studies are descriptions of patients' histories within a specific group. As such, doctors should not use them to choose treatment options. But case reports can help doctors think of new ideas for research studies in the future.

Cross-sectional studies. These studies look at how diseases interact with other factors within a specific group at one point in time. For example, a study might evaluate how patients who took a certain medication are doing ten years later to see who has and has not developed cancer. Because these studies only measure a point in time, they cannot prove that something causes cancer, but they can help scientists with future research.

What are cancer research review articles?

Medical journals publish many cancer research studies each year. This is good for adding to the scientific knowledge about cancer that lead to better treatment and care. However, the fast pace makes it hard for doctors, people with cancer, and caregivers to keep up with all of the new advances. Research studies are always shaping and reshaping the scientific understanding of cancer. But no single study is the final word on a type of cancer treatment. As a result, review articles are very helpful. Review articles study and sum up the findings of already published research on a certain topic.

Types of review articles include:

Systematic reviews. These articles summarize the best existing research on a specific topic at that time. Researchers use an organized method to find, gather, and review a number of research studies on a topic. By combining the findings of these studies, researchers can draw more reliable conclusions.

Meta-analyses. These articles combine data from several research studies on the same topic. This lets researchers find trends that are hard to see in single studies.

How do I know if cancer research results are reliable?

These questions can help you evaluate the quality of research study results:

  • Was the study peer-reviewed by the journal that published it? Peer review means that researchers who are not a part of the study looked over and approved the study's design and methods. Results from a study are more reliable if they are peer-reviewed. Learn more about peer review.

  • How long did a study last and how many people took part? A study is more useful and credible if the same results occur in many people over time. However, this rule does not apply to studies of rare types of cancer or cancer that is hard to treat. This is because there are fewer people to study. Also, cancer prevention trials are often much longer than treatment clinical trials. This is because it often takes longer to find out if a prevention strategy works compared to treatment of an existing cancer.

  • What is the phase of a new treatment study? Phase I and phase II clinical trials often tell researchers more about the safety of a treatment than how well it works. These studies tend to have less people than phase III clinical trials. Phase III clinical trials compare a new treatment with the standard of care. Doctors consider phase III clinical trials to be the most reliable.

  • Does the study overstate or oversimplify its results? Each study is a small piece of the cancer research puzzle. Medical practice rarely changes because of the results of 1 study. New results are exciting. But other researchers must confirm the results before the medical field accepts them as fact. Review articles are of special interest.

Questions to ask your health care team

Some patients decide to gather research study findings that may apply to their type and stage of cancer. Always talk with your health care team about how a specific study may or may not relate to your treatment plan. It is important to not stop or change your current treatment based only on something you read.

Consider asking your health care team these questions:

  • I saw a study about a new treatment. Is this treatment related to my type and stage of cancer? Were people like me included in that study?

  • What publications can I read to learn more about my cancer type ?

  • Are there medical journals that focus on the type of cancer I have?

  • Should I think about joining a clinical trial?

  • What clinical trials are open to me? Where are they located, and how do I find out more about them?

Related Resources

Understanding the Publication and Format of Cancer Research Studies

Medical News: 8 Ways to Separate Fact from Fiction

What to Know When Searching for Cancer Information Online: An Expert Perspective

Evaluating Cancer Information on the Internet

What Is a Cancer Research Advocate?