Cell-Free DNA Concentration as a Mutation-Agnostic Readout of Systemic Tumor Burden and Prognosis: A Prospective Analysis of 1,000 Patients

Background: Objective assessment of tumor burden in patients with solid tumors remains inexact. Furthermore, while mutation-based liquid biopsies are specific, they are limited by tumor heterogeneity and the requirement for detectable clonal mutations. Cell-free DNA (cfDNA) concentration, a cost-effective substrate for mutation-focused liquid biopsy, has shown promise as a "molecular tumor burden" biomarker. Methods: We analyzed cfDNA concentration from 1000 unique cancer patients using standardized protocols. Demographics, AJCC stage, clinical anatomic tumor burden and oncologic outcome variables were collected. Associations were assessed with non-parametric tests. Multivariable linear regression and Cox proportional hazards models were used to identify independent predictors and survival associations. Results: CfDNA concentration varied broadly (median 6.25 ng/mL; range 0.5-1132.9). Anatomic tumor burden, including tumor number (rho=0.25, p<0.0001) and largest tumor diameter (rho=0.25, p<0.0001), correlated significantly with cfDNA, especially in stage IV disease. Primary tumor site influenced cfDNA levels, with liver/bile duct cancers having higher cfDNA than other sites (median 13.5 vs 6.1 ng/mL, p<0.0001). Multivariable analysis confirmed overall tumor burden and hepatic tumor location (primary or metastatic) as principal drivers of cfDNA. Critically, cfDNA concentration was an independent predictor of shorter PFS (p=0.001) and DSS (p<0.0001), demonstrating increased value in advanced disease settings, irrespective of treatment intent. Conclusions: CfDNA concentration is a robust, biologically integrated biomarker that provides an objective measure of total systemic tumor burden and prognosis in a large, pan-cancer cohort. By capturing disease activity irrespective of mutational status, it offers a valuable adjunct to targeted profiling, particularly in heterogeneous or advanced malignancies. Although these findings require prospective clinical validation, cfDNA concentration may eventually augment patient selection for aggressive versus palliative interventions, especially in advanced disease.