Preoperative Plasma Cell-Free DNA Integrity Index in Clear Cell Renal Cell Carcinoma: An Exploratory Case–Control Study

Background/Objectives: Evaluation of renal tumour masses relies on conventional imaging, which cannot reliably characterise the histopathological type, and no validated blood-based diagnostic marker is available for renal cell carcinoma. The cfDNA integrity index, the ratio of long to short circulating cell-free DNA (cfDNA) fragments, may reflect the necrotic origin of tumour-derived DNA and is a candidate qualitative marker of malignancy. This exploratory, single-centre case–control study assessed the preoperative plasma cfDNA integrity index in patients with clear cell renal cell carcinoma (ccRCC). Methods: Plasma concentrations of 90 bp and 222 bp cfDNA fragments were measured by quantitative real-time PCR (qPCR) in 46 patients with histopathologically confirmed ccRCC (before surgery) and 17 healthy volunteers; the two groups were a convenience sample, were not matched, and differed in age and body-mass index. The cfDNA integrity index was defined as the ratio of the 222 bp to the 90 bp fragment concentration. Results: The cfDNA integrity index was higher in patients with ccRCC than in controls (median 0.28 vs. 0.15; p < 0.001, Mann–Whitney test) and rose progressively across healthy, non-metastatic (M0) and metastatic (M1) groups (p < 0.001, Kruskal–Wallis test; M0 vs. M1 p = 0.004). In unadjusted ROC analysis, both the integrity index (AUC 0.83, 95% CI 0.72–0.94) and its long 222 bp fragment component (AUC 0.93) discriminated patients with ccRCC from healthy volunteers, and the index separated metastatic from non-metastatic disease with an AUC of 0.79 (95% CI 0.64–0.88). The index was higher in high-grade (Fuhrman G3 + G4) tumours (p = 0.04) and in tumours with lymphovascular invasion (p < 0.001), and correlated with primary-tumour diameter. Conclusions: In this exploratory cohort, the preoperative plasma cfDNA integrity index was higher in patients with ccRCC than in healthy volunteers and was associated with several adverse pathological features; these findings require confirmation in larger, matched studies that include benign renal masses before any diagnostic role can be claimed.