What kinds of trials are available?

There are a huge number of trials out there, and it’s important to understand the different trial phases and types you may come across in your research. Not all trials focus on treatment efficacy, but most of what we cover in this Learning Center is most relevant to treatment trials. It’s important to know what your goals are when looking for clinical trials. This guide will help you understand the basics.

It’s important to note that we focus on US clinical trials in this section. If there are any words you don’t understand, check out the glossary here.

What types of trials are there?


These trials look at different ways for preventing disease. If you already have cancer, it’s unlikely you will be eligible for prevention trials. However, there are prevention trials that look at cancer recurrence — so those with a prior cancer diagnosis may qualify for some prevention trials.


These trials aim to develop new tests and tools for screening and diagnosing illnesses.


Treatment trials test new drugs and other treatment methods — such as new approaches to radiation and surgery — to see how well they work in treating diseases. All treatment trials are interventional.


Behavior trials look at the way in which lifestyle changes can affect overall well-being. Behavioral trials can be interventional (where researchers ask you to do a new behavior) or observational, where your behavior will simply be recorded.

Quality of life

These trials look at different ways to improve patients’ quality of life over time. Quality of life trials can also focus on improving management of treatment side effects.

What are the different trial phases, and what do they mean?

Trials in all phases have safeguards, and provide both risks and benefits. Phases are a way for researchers to describe different research objectives in the drug development process. Currently, most trials for CRC patients are phase I or phase II.

It’s important to note that what defines the overall success or failure of a trial for researchers may be very different from individual patient experiences. You may see great benefit from an “unsuccessful” trial, or a treatment tested in a trial considered successful may not work for you. 

Phase I

In phase I trials, researchers test a drug on a small number of patients, usually between 20 and 80. In this phase, the goal is to test safety and learn more about side effects. This drug or drug combo will already have been tested for safety in the laboratory and in animals.

The aim of a phase I trial is to find out the doses at which the drug being tested will start to have severe side effects for patients. After this limit is known, the drug is tested in a dose expansion cohort, where researchers reduce dosing and test for efficacy and side effects in patients. Patients are monitored closely throughout the trial to catch and treat any side effects as soon as they arise. 

Knowing how many patients have already enrolled in a phase I trial can give you some idea about how much information is already known about dosing.

All patients in phase I trials receive the experimental treatment and will be monitored for efficacy. While phase I trials do not have a control arm, they may have multiple experimental arms. If a treatment isn’t working for a patient, they will be removed from the trial as they would in any other phase trial.

Learn more about phase I trials here:

Phase II

In phase II trials, researchers test the trial drug on a larger number of patients, usually between 100 and 300. In this phase, researchers test the drug for effectiveness, and to learn more about side effects in a larger population. Compared to phase I trials, in phase II trials there are more knowns and fewer uncertainties. 

All patients in phase II trials receive the experimental treatment and will be monitored for efficacy. While phase II trials do not have a control arm, they may have multiple experimental arms testing different drug combinations, dosing amounts, or dosing schedules.

Phase III

In phase III trials, the drug is given to an even larger number of patients (often 1000 to 3000) in order to confirm its effectiveness. Researchers will also continue to monitor for safety and side effects.

However, in phase III trials, the experimental treatment is compared with standard-of-care treatment to figure out how the new drug or combination behaves. So you may or may not get the experimental treatment.

Patients are usually randomized into an experimental arm or a standard-of-care arm. If both the patient and doctor know which arm the patient is on, that is called an open-label trial. If the doctor knows what arm a patient is on, but the patient does not, that is called a blind trial. If neither the doctor nor patient knows which arm a patient is on, this is called a double-blind trial. Understanding the chances of being randomized into each trial can affect your decision-making process. 

What if I don’t live in the US?

While the US has a huge number of clinical trials, there are trials run all over the world. Some of them can be found on clinicaltrials.gov, but the best way to learn about them is to ask your team for advice. If you are located in Canada, the video below gives a good summary of the types of clinical trials happening there.

Clinical trials in Canada:

Curious about clinical trials?

Join one of our COLONTOWN Facebook groups:

  • In Tom’s MSI-H Clinic, we discuss treatments and trials for MSI-H patients
  • In Tom’s MSS Clinical Trials, we chat about trials open to mSS patients
  • In Tom’s NIH Lounge, we discuss trials run by the National Institute of Health (NIH)
  • Check out Across the Pond where you can find information on treatment in Europe

Want to join? Fill out the registration form here.

COLONTOWN University has so much more to offer, from DocTalk videos with CRC experts to easy-to-understand biomarker test breakdowns. We’re here for you! See our list of Learning Centers here.