Eligibility will depend upon the scientific design of each specific clinical trial. Based on the research question the trial is seeking to answer, certain patients will, or will not, be eligible to join. 

Common criteria include the particular stage and type of cancer the patient is fighting, demographic factors such as age, and what types of treatments the patient has received in the past. Limiting participation to a specific group of people enables researchers to obtain more accurate and meaningful research results. 


Participant criteria are also an important part of patient safety. If, for example, a patient has another pre-existing health condition besides cancer, a clinical trial could worsen the symptoms of that ailment and put the patient at increased risk.