Limitations and Result Interpretation

Despite its strong specificity, Galleri® is not a diagnostic test. This article covers false-result probabilities, stage-dependent sensitivity and the result interpretation framework.

False Positives and False Negatives

• False positive: a signal is detected but further work-up finds no cancer. Even with 99.5%+ specificity, in low-prevalence populations the positive predictive value sits in the 66–77% band; i.e. for every 3–4 people with a detected signal, further work-up may not show cancer in one of them.
• False negative: no signal is detected although cancer is present. Sensitivity is low particularly at early stages (16.8% at Stage I); a negative result does not eliminate risk.
• Non-cancer signals: conditions such as chronic inflammation or organ damage can also produce abnormal methylation signals.

Stage-Dependent Sensitivity

In CCGA3 data, sensitivity is 16.8% at Stage I and 90.0% at Stage IV. This trend shows the test's screening power alongside its insufficiency on its own: a negative result does not replace clinical suspicion; a positive result does not replace a definitive diagnosis.

Pathway When a Signal Is Detected

1. Targeted imaging/specialty planning with the CSO prediction (e.g. lung signal → low-dose CT + pulmonology).
2. If initial work-up is negative, the clinical follow-up protocol continues; whole-body imaging may be evaluated if needed.
3. Diagnostic confirmation is always made with tissue/histological examination.

Situations of Non-Use

• Symptomatic patients (weight loss, bleeding, pain etc.): the diagnostic pathway takes priority.
• Patients undergoing active cancer treatment.
• Serial monitoring use: the test is not designed for monitoring; disease course tracking is done with different tests (e.g. CTC, ctDNA).

This content is for educational purposes and does not constitute medical advice. Results must be interpreted through physician evaluation.