Understanding Cancer Research Study Design and How to Evaluate Results
Approved by the Cancer.Net Editorial Board, 04/2018
Doctors and scientists conduct research studies to find better ways to prevent and treat cancer. Depending on the questions they want to answer, researchers can design these studies in different ways. No study design is perfect. Each has strengths and drawbacks. It is important to understand a study’s design. By doing this, you can understand the results to know if they apply to your situation.
In cancer research, there are 2 main types of research studies:
- Experimental studies. This type of study provides an intervention, such as a new treatment. The intervention is given to a group of people. Then, researchers compare their results to those of another group that does not receive the intervention. This other group is known as the control group. The researchers choose who does and does not receive the intervention either randomly or through a selection process. Experimental studies help researchers learn more about how cancer starts or spreads. These studies can also test new imaging techniques and explore quality of life issues.
- Observational studies. This type of study involves observing groups of people in a natural setting and looking at a specific result. A result may include whether 1 group of people has more cancer diagnoses than another group. In these studies, the researchers cannot control the intervention, such as a person’s weight or whether they took vitamin supplements. These studies are often described as epidemiologic. Epidemiology involves studying how different risks cause or spread a disease in a community.
Types of experimental studies
Experimental studies are more reliable than observational studies. This is because the volunteers are placed in the intervention or control group by chance. This reduces the likelihood that the assumptions or preferences of the researchers or volunteers will change the study results. Such assumptions or preferences are called bias.
This type of study also helps researchers to better find and control other factors, such as age, sex, and weight. These factors can affect the results of the study.
Researchers may also consider certain factors when choosing people to enroll in an experimental study. They could be based on type of cancer, stage of the disease, or whether the cancer has spread.
One of the most common types of experimental studies is the clinical trial. This is a research study that tests a medical intervention in people. Clinical trials test:
- The effectiveness or safety of a new drug or combination of drugs
- A new approach to radiation therapy or surgery
- A new treatment or way to prevent cancer
- Ways to lower the risk of cancer coming back
Doctors and researchers conduct clinical research in segments called phases. Each phase of a clinical trial provides different answers about the new treatment. For instance, it can show the dose, safety, and efficacy of the treatment. The efficacy is how well the treatment works. There are 4 phases of clinical trials.
In a clinical trial, volunteers are usually selected by chance to either be in the treatment or control group. Researchers can prevent bias in a clinical trial by keeping volunteers and/or themselves from knowing how the volunteers are grouped. This is a process known as “blinding.”
Types of experimental studies include:
- Double-blind randomized trial. Most scientists believe this type of clinical trial will produce the best evidence in a study. Neither the volunteers nor the researchers know who belongs to a treatment or control group until the study ends.
- Single-blind randomized trial. In this type of trial, the volunteers do not know whether they belong to a treatment or control group. But the researchers know.
- Open/unblinded trial. Both volunteers and researchers know who belongs to each test group in this type of study. This occurs when it is not possible to use blinding. For instance, the study could compare a surgical treatment to a drug.
Types of observational studies
In observational studies, researchers have less control over the study volunteers. This means that certain factors could affect the results. These studies, however, are useful in providing initial evidence that can help guide future research.
Types of observational studies include:
- Case-control studies. These types of studies compare 2 groups of people. For instance, they could compare those who have cancer (the case) and those who do not (the control). Researchers may look for lifestyle or genetic differences between the 2 groups. By doing this, they hope to find out why 1 group has a disease and the other group does not. These studies are conducted retrospectively. That is, they are researching what has already happened.
- Cohort studies. These studies are prospective, which means that researchers study the event as it occurs. They monitor a group of people for a long time and track something. For example, they could track any new cancer diagnoses. This type of study can assess whether certain nutrients or actions 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. These studies are detailed descriptions of a patient’s medical history. The individual patient descriptions are called case reports. If many patients receive a similar treatment, the case reports may be combined into a case series. The results of case series studies are descriptions of patients’ histories within a specific group. As such, they should not be used to determine treatment options.
- Cross-sectional studies. These studies examine how diseases interact with other factors within a specific group at a point in time. But because these studies only measure interactions at a single point in time, they cannot prove that something causes cancer.
Types of review articles
A large number of cancer research studies are published every year. Given this, it is challenging for doctors, as well as interested patients and caregivers, to keep up with the latest advances. Research studies published in journals are constantly shaping and reshaping the scientific understanding of that subject. No single study provides the final word on a topic, type of cancer, or treatment. As a result, review articles, which evaluate and summarize the findings of all published research on a certain topic, are extremely helpful.
Types of review articles include:
- Systematic reviews. These articles summarize the best available research on a specific topic. Researchers use an organized method to locate, gather, and evaluate a number of research studies on a particular topic. By combining the findings of a number of studies, researchers are able to draw more reliable conclusions.
- Meta-analyses. These studies combine data from several research studies on the same topic. By combining these data, a meta-analysis can find trends that are hard to see in smaller studies. But if the single studies were poorly designed, the results of the meta-analysis may not be useful.
Evaluating research studies
Here are some tips for finding out the quality of a research study:
- Find out if the journal uses a peer-review process. Results from a study are more reliable if they are peer-reviewed. This means that researchers who are not a part of the study have looked over and approved the design and methods.
- Look at the length of the study and the number of people involved. A study is more useful and credible if the same results occur in many people across a long time. Studies of rare types of cancer or cancers with a poor chance of getting better are an exception to this rule. This is because there are a small number of patients to study. Also, when looking at the length of the study, it may be suitable for some clinical trials to be shorter. For instance, cancer prevention trials are often much longer than treatment clinical trials. This is because it usually takes longer to figure out if a prevention strategy is working compared to a treatment.
- Consider the phase of the study when learning about new treatments. Phase I and II clinical trials usually tell you more about the safety of a treatment and less about how well it works. These studies tend to have a smaller number of patients compared to phase III clinical trials. Phase III clinical trials compare a new treatment with the standard of care. “Standard of care” means the best treatments known. Doctors consider phase III clinical trials to be the most reliable.
- Find out if the study supports or contradicts current research. New results are exciting, but other researchers must validate the results before the medical field accepts them as fact. Review articles like systematic reviews are of special interest. They review and draw conclusions across all of the published research on a specific topic.
- Watch out for conclusions that overstate or oversimplify the results. Each study is a small piece of the research puzzle. Medical practice rarely changes because of the results of a single study.
Questions to ask your health care team
Always talk to your health care team about what you find in an abstract or study. If you have reviewed a study that suggests a different approach to cancer treatment, do not stop or change your treatment. First talk with your health care team about how the study relates to your treatment plan.
Consider asking your health care team the following questions:
- I recently heard about a study that used a new treatment. Is this treatment related to my type and stage of cancer?
- What type of journals should I read to learn more about my type of cancer?
- Should I consider being a part of a clinical trial?
- What clinical trials are open to me?
- Where can I learn more about clinical trials?