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What are Clinical Trials

Clinical trials are medical research studies that require patient participation and aim to answer medical questions, usually concerning a new treatment for a particular disease. These trials are the final stages of an extensive drug development process and are essential for the development of new, potentially life-changing treatments. Many of the treatments available today are the result of clinical trials.

Clinical trials are important in osteosarcoma because not all osteosarcoma patients respond to chemotherapy (standard treatment for osteosarcoma) and alternative options are limited. Therefore, clinical trials are essential to discover new treatments that improve outcomes in the osteosarcoma community.

It is always your decision whether to take part in a clinical trial and whether a trial is right for you is very dependent on the trial. Visit our frequently asked questions page to find out more about taking part in a clinical trial.

On this page you will find information on

Drug Development

Clinical Trial Phases

Types of Clinical Trial 

Trial Status 

Drug Development

Basic Research

Lab-based research to better understand how the human body works and how diseases develop.

Drug Discovery

Finding a compound (drug) to block a gene or protein that is involved in disease development

Pre-Clinical Research

Testing a new drug on non-human subjects to assess its safety and effectiveness. 

Clinical Research

Testing a new drug in clinical trials to determine its safety and effectiveness in humans. 


Regulatory bodies approve the use of the drug in medical practice.

Clinical Trial Phases

Phase 1


Tests safety, dose and best way to give drug(s)

 Small number of people (20-  100).

Phase 2

Tests effectiveness and side effects.

Moderate number of patients (50-300).

Phase 3

People being given tablets

Tests effectiveness and side effects.

Large group of patients (100s-1000s).

Phase 4 


Occurs once the drug is approved and determines long term risks and benefits.

Phase 1: A phase 1 trial assesses the safety and dose of a new drug(s). In other words, it determines the dose at which the drug may have the most benefit but with tolerable side effects. Phase 1 trials involve a small number of participants, and the drug will usually be given at a lower dose first and then increased (dose escalation). This means side effects can be closely monitored, and the dose escalation stopped if side effects reach a certain threshold. Although the aim is not to assess the effectiveness of the drug some patients do benefit.

Participants in phase 1 trials are often the first humans to trial the drug ever or for a particular condition. The drug will have undergone extensive safety testing and all participants will be monitored very closely for side effects throughout the trial. These trials are required to move to phase 2 and are an essential part of drug development.

Sometimes phase 1 trials are split into phase 1a/1b.

1a –  Determines the highest dose with tolerable side effects and phase1b

1b – The dose is tested in other participant groups

Phase 2: A phase 2 trial assesses the effectiveness of a new drug. The dose of the drug will have been predetermined by a phase 1 trial and although the safety profile will have been approved, side effects will continue to be monitored. Phase 2 trials can consist of a single-arm where all participants will receive the new drug or multiple arms where participants will usually be randomised to get the drug or an alternative intervention such as a placebo or standard treatment. Drugs can be licenced for use after phase 2 trials if results are promising especially in a rare condition where conducting a larger trial is challenging, or if there is an urgent need for new treatments.

Phase 3: Phase 3 trials are usually a continuation of a phase 2 trial but on a larger scale and are often the pre-requisite for licencing drugs.

Phase 4: Phase 4 studies are performed after a dug has been licenced and are in use. They investigate the long-term effects of treatment and how best to optimise its use.

Types of Clinical Trial

Interventional Study: An Interventional study is the most common type of clinical trial and is done to determine the dose, safety and effectiveness of a new treatment. Patients will therefore be given an intervention normally in the form of a drug and its effects will be monitored.

Observational Study: An Observational study follows a particular group of patients to answer a question(s) about a condition and/or treatment under normal conditions. No intervention is given, and the patients do not deviate from their treatment plan. For example, answering questions about what countries certain conditions are more prevalent in can help doctors to identify certain risk factors (i.e sun exposure, diet) and recommend how to reduce the risk.

Patient Registry: A registry collects data about a certain population to be used in future research. The data collection often includes both demographic data such as age, ethnicity and sex and clinical data such as date of diagnosis and blood results. Data can be inputted by patients, doctors or both depending on the study.

Expanded Access: These are drugs that have not yet been licenced but are approved for use in either a specific individual or patient group who usually have limited treatment options. Although not licenced, these drugs will have shown promise in early clinical trials.

Trial Status 


Recruiting – Trials that are currently recruiting people.   

Active, not recruiting – Trials that are ongoing but are not recruiting people.

Not yet recruiting – Trials that have not yet started recruiting people.

Terminated – Trials that have stopped. This could be due to loss of funding or side effects from the drug.  

Completed – Trials that have finished.

Unknown – Trials whose status is unknown.

“We are looking into developing an immunotherapy for osteosarcoma…using viruses that attack cancer cells”

Professor Graham Cook, University of Leeds

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