Most adults with a confirmed cancer diagnosis are potentially eligible for at least one clinical trial, though every study has its own set of criteria that determine who can enroll. Eligibility depends on factors like your cancer type and stage, your overall physical fitness, specific lab results, and what treatments you’ve already received. Understanding these requirements can help you figure out which trials to pursue and what to expect during screening.
The Basics: Cancer Type, Stage, and Diagnosis
Every cancer clinical trial specifies which types and stages of cancer it’s studying. A trial for advanced lung cancer won’t enroll someone with early-stage breast cancer, for example. Most trials in non-curative settings focus on cancers that are unresectable (can’t be surgically removed), locally advanced, or metastatic, meaning the cancer has spread. For blood cancers, trials typically target diseases with poor long-term survival.
You’ll need a confirmed diagnosis, usually through a biopsy or imaging, before any trial will consider you. Many trials also require that you’ve already tried standard treatments known to work for your cancer. If a well-established cure exists for your type of cancer, such as certain childhood leukemias, Hodgkin lymphoma, or testicular cancer, you’re generally expected to have tried that first.
Physical Fitness and Performance Status
One of the most important eligibility factors is your “performance status,” a simple rating of how well you can handle daily activities. Doctors use two main scales: the ECOG scale (scored 0 to 4, with 0 being fully active) and the Karnofsky scale (scored 0 to 100, with 100 being fully active). Lower performance status correlates with worse survival and a harder time tolerating experimental treatments, so many trials set minimum thresholds.
Historically, trials have been limited to high-functioning patients with ECOG scores of 0 or 1. In studies leading to FDA drug approvals between 2009 and 2023, patients with an ECOG score of 2 made up only about 4.3% of participants on average, even though many real-world cancer patients fall into that category. The FDA now recommends that patients with ECOG 2 (or Karnofsky 60 to 70), meaning people who are up and about more than half the day but unable to work, should be included in trials unless there’s a specific safety reason not to. Early-phase studies tend to be more flexible here: about 41% include patients with lower performance scores, compared to only 20% of phase 3 trials.
Biomarker and Genetic Testing
A growing number of trials require specific molecular characteristics in your tumor. If a drug targets a particular genetic mutation or protein, the trial will only enroll patients whose cancers carry that feature. For instance, some lung cancer trials only accept patients with certain changes in the EGFR gene, while some breast cancer trials require HER2-positive status.
This is where biomarker testing becomes critical. Some trials, called basket trials, enroll patients based entirely on the genetic changes in their cancer rather than where in the body it started. The NCI-MATCH program, for example, matches patients to treatments based on specific mutations found through tumor sequencing. If you haven’t had biomarker testing done, it’s worth asking your oncologist about it, since the results could open doors to trials you wouldn’t otherwise know about.
Lab Values and Organ Function
Before enrolling, you’ll go through blood work and other tests to confirm your organs are functioning well enough to handle the experimental treatment. Trials commonly check liver function, kidney function, and blood cell counts. A trial testing a drug that’s processed by the kidneys, for example, will require adequate kidney function. One studying a drug that could stress the liver will check liver enzymes and bilirubin levels.
The FDA has pushed for these thresholds to be set based on the specific drug being tested rather than applying blanket restrictions. If an experimental drug doesn’t affect the liver and isn’t processed there, overly strict liver function cutoffs just exclude people unnecessarily. In practice, though, you should expect lab screening as part of the enrollment process, and borderline results can sometimes be re-tested.
Prior Treatment and Washout Periods
Trials need to know that any side effects you’re experiencing come from the experimental drug, not leftover effects of your last treatment. For this reason, many require a gap, called a washout period, between your most recent therapy and enrollment. Historically, about half of cancer trials required a washout of 14 to 28 days, with some going as long as three months.
This approach is changing. A joint recommendation from the American Society of Clinical Oncology and Friends of Cancer Research now advises that fixed time-based washout periods should be removed in most cases. Instead, eligibility should be based on whether you’ve actually recovered from significant side effects of your previous treatment. For brain radiation specifically, a standard 14-day washout after stereotactic or whole-brain radiation is still recommended. But the old blanket rule of waiting 28 days after chemotherapy is no longer considered scientifically necessary for many trials.
Common Reasons People Are Excluded
Beyond the cancer-specific criteria, trials frequently exclude patients based on several other health factors:
- Prior cancers: Many trials exclude people who had a different cancer within the past 3 to 5 years. Exceptions are commonly made for low-risk cancers like non-melanoma skin cancer, cervical carcinoma in situ, or early prostate cancer treated with surgery alone.
- Chronic infections: HIV, hepatitis B, and hepatitis C have traditionally been grounds for exclusion, though this is changing significantly (more on this below).
- Autoimmune diseases: Conditions like lupus, rheumatoid arthritis, or scleroderma can be exclusionary, particularly for immunotherapy trials where the treatment stimulates the immune system.
- Psychiatric conditions and substance use disorders: Some trials exclude patients with major psychiatric illness or active substance abuse, often out of concern about the ability to follow the study protocol.
HIV, Hepatitis B, and Hepatitis C
Patients with these chronic infections were routinely excluded from cancer trials for decades. The FDA now recommends a much more inclusive approach. For HIV-positive patients, those with CD4+ T-cell counts of 350 or higher should generally be eligible for any cancer trial. Even patients with lower counts can qualify if they have a potentially curable cancer or if the drug being tested is further along in development. Patients without a history of AIDS-related infections should generally be eligible across the board, and those who had such infections more than 12 months ago can often qualify as well.
The rationale is straightforward: excluding these patients means trial results don’t reflect the real-world population that will ultimately use the drug. Including them generates safety and efficacy data for patients who need it most.
Age Requirements: Children and Older Adults
Most adult cancer trials set 18 as the minimum age. However, the FDA encourages sponsors to consider including adolescents ages 12 to 17 in adult trials when the disease and drug target are appropriate. Children under 12 require more specialized protocols, and children under 2 are almost never included in adult trials due to the vulnerability of their developing organs and metabolism.
For minors, federal regulations require that the trial offer the prospect of direct benefit to the child, that the benefit-risk balance is at least as favorable as existing treatments, and that the child’s assent (agreement) and a parent’s or guardian’s permission are both obtained. An institutional review board must verify all of these safeguards before any child can participate.
There is no standard upper age limit for cancer trials. Older adults are not automatically excluded, though performance status and organ function requirements may screen out some older patients indirectly. The FDA now requires that sponsors of phase 3 and other pivotal trials submit a Diversity Action Plan with enrollment goals broken down by age group, among other demographics, specifically to address the historical underrepresentation of older patients and other groups.
Diversity Action Plans and Broader Access
Since the passage of the Food and Drug Omnibus Reform Act in December 2022, sponsors of phase 3 cancer trials and certain pivotal device studies must submit a Diversity Action Plan to the FDA. These plans must include enrollment goals disaggregated by race, ethnicity, sex, and age, along with an explanation of how those goals will be met. This requirement exists because trial populations have historically skewed younger, whiter, and more male than the actual cancer patient population.
For patients, this means trial teams are actively working to broaden who gets enrolled. If you’ve assumed clinical trials weren’t designed for someone like you, the landscape is shifting. Asking your care team about available trials, or searching databases like ClinicalTrials.gov, is increasingly likely to turn up options that match your specific situation.
How Eligibility Differs by Trial Phase
Phase 1 trials test safety and dosing in small groups and tend to have the broadest eligibility criteria. They’re more likely to accept patients with lower performance status or those who’ve been through multiple prior treatments. Phase 2 trials narrow the focus somewhat, looking at whether the drug works against a specific cancer. Phase 3 trials, which compare the new treatment to the current standard, are typically the most restrictive because they need to mirror the intended real-world patient population while controlling for variables that could muddy the results.
That said, the FDA has been pushing phase 3 trials to loosen up. The recommendation to include patients with ECOG performance status of 2, the shift away from rigid washout periods, and the new diversity requirements all aim to make later-phase trials more accessible without compromising the science.