Fox Chase Cancer Center released phase 2 RETAIN‑2 results showing a circulating tumor DNA (ctDNA) blood test can identify muscle‑invasive bladder cancer patients with low metastatic risk who might safely avoid immediate radical cystectomy. The study supports ctDNA as a predictive biomarker for treatment de‑escalation in selected patients. ctDNA refers to tumor‑derived DNA fragments detectable in plasma; when used as a minimal residual disease or risk stratification tool, ctDNA can help personalize surgical and systemic treatment decisions.