Two separate studies strengthened circulating‑tumor‑DNA (ctDNA) as a clinical biomarker. A Phase I study using Personalis’ NeXT Personal MRD assay found that early declines in tumor‑informed ctDNA predicted progression‑free and overall survival across metastatic solid tumors treated with immune checkpoint inhibitors; ctDNA clearance correlated with large PFS gains and prolonged OS in MRD‑negative patients. The team recommended initiating monitoring as early as possible to guide treatment decisions. Complementing plasma work, Droplet Biosciences validated postoperative lymph‑fluid ctDNA as a sensitive sample type to detect molecular residual disease in head and neck cancer, outperforming time‑matched plasma for locoregional relapse detection. The lymph‑fluid approach showed higher early sensitivity for locoregional recurrence; investigators noted potential utility in tailoring adjuvant therapy decisions. Clarification: ctDNA refers to tumor‑derived DNA fragments circulating in body fluids that can serve as an early signal of response or residual disease.