A new study shows that circulating tumor DNA (ctDNA) can predict the effectiveness of immunotherapy in advanced Melanoma just 3–4 weeks after treatment starts—much faster than standard scans. Using the tumor-informed Signatera assay, doctors can track tumor DNA fragments in the blood to monitor response in real time.
Early changes in ctDNA were strongly linked to outcomes. A decrease at 3–4 weeks was associated with a 23-fold higher chance of response and an 82% lower risk of progression. Patients whose ctDNA became undetectable early had a 1-year survival rate above 90%, while an early increase predicted poor outcomes, with median progression-free survival of only 2.3 months.
The method also helps resolve “pseudo-progression,” where tumors appear larger on scans due to immune activity. If ctDNA is falling, doctors can be confident the treatment is working. Clinically, early ctDNA monitoring could guide faster therapy adjustments, enrollment in clinical trials, or reduced imaging and treatment intensity for patients responding well.