How to read clinical trial eligibility criteria

Every clinical trial has a list of eligibility criteria that determine who can enroll. These criteria are published on ClinicalTrials.gov and usually include 10 to 30 specific requirements. Reading them requires understanding a small vocabulary of oncology terms and the general structure criteria follow. Once you can parse them, you can determine whether a trial is plausibly a fit for your situation before calling the site.

This guide walks through the common criteria categories and explains what each one means.

The structure of eligibility criteria

A typical trial listing on ClinicalTrials.gov has two sections:

• Inclusion criteria. Requirements you must meet to qualify. Examples: “histologically confirmed non-small cell lung cancer,” “at least 18 years of age,” “ECOG performance status 0 or 1.”
• Exclusion criteria. Conditions that disqualify you. Examples: “prior treatment with immunotherapy,” “active autoimmune disease,” “symptomatic brain metastases.”

You must meet every inclusion criterion and no exclusion criterion.

Common criteria categories

Diagnosis

The trial specifies exactly which cancer type, subtype, and stage it is enrolling. Examples:

• “Histologically or cytologically confirmed [cancer type]” means the diagnosis must be confirmed by pathology, not just suspected on imaging.
• “Stage IV” or “metastatic” means the cancer has spread beyond the original site.
• “Locally advanced” generally means the cancer has spread to nearby tissues or lymph nodes but not distant sites.
• “Recurrent” means the cancer has returned after initial treatment.
• “Refractory” means the cancer has not responded to prior therapy.

Biomarker requirements

Many modern trials require specific molecular markers:

• “EGFR mutation positive”: lung adenocarcinoma with a specific mutation in the EGFR gene.
• “HER2-positive” or “HER2 3+”: amplified or overexpressed HER2, common in about 15 to 20 percent of breast cancers.
• “BRCA1/2 mutation”: germline or somatic mutation in BRCA genes.
• “PD-L1 expression ≥ [percentage]”: tumor expresses PD-L1 at a specified level, used to guide immunotherapy trials.
• “Microsatellite instability high” (MSI-H) or “mismatch repair deficient” (dMMR): tumors with DNA repair defects, often eligible for immunotherapy.
• “KRAS G12C mutation”: a specific mutation in the KRAS gene, relevant for sotorasib and similar targeted therapies.

If you do not know your biomarker status, biomarker testing is often the first step. Some trials provide testing as part of screening.

Performance status

Performance status measures how well a patient can perform normal activities. Two scales are commonly used:

• ECOG Performance Status: 0 (fully active) through 4 (completely disabled). Most cancer trials require ECOG 0 or 1; some allow ECOG 2.
• Karnofsky Performance Status: 0 to 100 scale. 100 means normal; 80 to 90 is consistent with trial eligibility in most oncology trials.

If you are hospitalized, bedbound, or dependent on others for all activities of daily living, most trials will not accept you.

Prior therapy rules

Trials commonly specify requirements about prior treatment:

• “At least one prior line of systemic therapy”: you must have received at least one previous treatment regimen.
• “No more than two prior lines”: you have not had too many prior treatments.
• “Treatment-naïve”: you have not had systemic treatment for this cancer before.
• “Washout period of [X] days”: time since last treatment before screening for the trial.

Lines of therapy count regimens, not individual drugs. A standard regimen of multiple drugs given together counts as one line.

Exclusion: other active conditions

Trials typically exclude patients with:

• Active infection requiring systemic therapy
• Uncontrolled heart disease (recent heart attack, unstable angina, severe heart failure)
• Active autoimmune disease (for immunotherapy trials especially)
• Active HIV, Hepatitis B, or Hepatitis C (for some trials; increasingly, these are allowed)
• Another active cancer requiring treatment
• Symptomatic brain metastases (asymptomatic and treated metastases are often allowed)
• Pregnancy or breastfeeding

Exclusion: prior specific therapies

Some trials exclude patients who have had certain prior treatments:

• “No prior treatment with [drug class]”: often seen in immunotherapy trials where prior PD-1/PD-L1 inhibitor exposure is disqualifying.
• “No prior treatment with [specific drug]”: a narrow exclusion specific to the investigational agent.
• “No radiation within [X] weeks of study start”: to avoid confounding imaging response assessments.

Laboratory values

Trials typically require specific laboratory values to ensure safety:

• Adequate bone marrow: white blood cell counts, platelets, hemoglobin above specified thresholds
• Adequate liver function: AST, ALT, bilirubin within specified limits
• Adequate kidney function: creatinine clearance or eGFR above specified threshold

How to evaluate whether you qualify

1. Read inclusion criteria first. Check whether your diagnosis, stage, biomarker status, performance status, and line of therapy match.
2. Then check exclusions. These are harder to assess without your full medical history in front of you. Check against active conditions, prior therapies, and recent treatments.
3. Look at specific numbers. Lab values, age limits, and timing of prior treatments are precise; you either meet them or you do not.
4. When in doubt, call the study coordinator. Every trial listing on ClinicalTrials.gov has contact information. Coordinators pre-screen candidates over the phone; they can often determine likely eligibility in one conversation.

Example: a real trial listing structure

A typical listing for an immunotherapy trial in non-small cell lung cancer might include:

• Inclusion: Histologically confirmed stage IV NSCLC; PD-L1 ≥ 1 percent; ECOG 0-1; at least one measurable lesion; adequate organ function per specified lab values; at least 18 years old.
• Exclusion: Prior anti-PD-1 or anti-PD-L1 therapy; active autoimmune disease; active Hepatitis B or C; symptomatic brain metastases; pregnancy.

A patient with stage IV lung adenocarcinoma, PD-L1 expression of 30 percent, ECOG 1, no prior immunotherapy, and good organ function would be a likely fit for screening.

What happens if you screen but do not pass

You can still participate in other trials. Not passing screening for one trial is not a red flag for others. Your oncologist or a dedicated trial navigator can help identify alternative trials. See how to find a clinical trial for search strategies.

Next

• How to find a clinical trial
• Clinical trial phases explained
• Insurance coverage for clinical trials: what the ACA requires
• Cancer biomarkers explained
• Clinical trials hub: active trials by cancer and state