There are several stages of clinical trials: phase 1, phase 2 and phase 3.

Phase 1 trials are small and experimental, and typically include approximately 20 to 100 healthy volunteers or patients with the target cancer of interest. The aim of phase 1 trials is to identify toxicity and a safe dosage of the drug. 

Phase 2 studies can last from several months up to several years. They recruit more patients than a phase 1 trial and further investigate potential adverse effects and the correct dosage for patients. If the phase 2 study meets its objectives, the new treatment may continue onto a phase 3 trial. 

Phase 3 clinical trials are larger and can last for several years – they may include several hundred to even several thousand patients with a particular cancer. The purpose of phase 3 trials is to evaluate the safety and efficacy of the drug in a larger group of people, and the results from these trials are typically used in the final application process.  

Once a new drug has successfully completed clinical trials, it will be submitted to the MHRA in the UK for authorisation. If licensed the drug company will then submit it to NICE in England and separately to the SMC in Scotland for use. This can lead to disparities across the UK where a drug might be available on the NHS in one country but not in another.