In clinical trials, patients must meet specific requirements, known as eligibility criteria, to participate. These criteria include characteristics a patient must have to be included in the study called inclusion criteria (e.g., a patient must be over the age of 18), and characteristics that would exclude a patient from being enrolled to the study called exclusion criteria (e.g., a no prior treatment for cancer).

Inclusion and exclusion criteria ensure that trial participants are similar in characteristics such as age, cancer type and stage, overall health status, and prior treatments to increase the likelihood that the study’s findings are due to the treatment being tested rather than other variables or random chance.

Eligibility criteria must be evidence based and carefully designed to allow for rigorous assessment of trial results while balancing the need for efficient trial conduct (i.e., enrollment and accrual) and representation of the patients who will use a treatment in the real-world. The stricter the eligibility criteria, the less diverse the study population becomes, which restricts the ability to generalize clinical trial findings to the broader population that will receive treatment outside of the study. For example, if a clinical trial for a new medication only includes participants between ages of 30 and 40 who are in perfect health, the results may not be applicable to older adults with existing health conditions who will also use the medication in real-world settings.