In most cases, “healthy” in clinical trials is defined as a person who does not have the condition indicated for the study drug (which in this case is cancer).
These studies include healthy volunteers to help scientists learn more about the specific study drug, such as how it is broken down by the body or if there are any side effects, before it is given to patients who have an active illness. This enables research to be done more safely, quickly, and at reduced cost compared to trials that only include patients, which ultimately helps patients once trials are completed.
It is often thought that cancer-related clinical trials are reserved for patients with severe illness or as a “last resort” due to potential risks associated with traditional therapies like chemotherapy, but this is not the case for many modern study drugs. Because of medical advancement, potential new medicines are often able to follow the same process as other non-cancer trials.