Circulating tumor DNA performance in primary retroperitoneal lymph node dissection: A stage-based analysis.

590 Background: Novel biomarkers appear to have use in the surveillance and treatment monitoring of testicular germ cell tumors (GCT). Recently, ctDNA has been demonstrated to detect GCT/teratoma in both primary and post-chemotherapy retroperitoneal lymph node dissection (RPLND), however the association of ctDNA levels by stage has not yet been determined. In this study, we sought to determine the utility of ctDNA for predicting active GCT on P-RPLND by comparing patients’ RPLND histology with their pre-operative ctDNA status in those with clinical stage I and II disease. Furthermore, we determined the association between ctDNA levels and clinical stage at RPLND. Methods: Patients undergoing primary (P-RPLND) from March 2023 to October 2025 had prospectively collected plasma ctDNA assay. Patients were stratified by clinical stage (CS) based on pre-operative cross-sectional imaging. The association between ctDNA positivity and P-RPLND histology was assessed. Test statistics were calculated for ctDNA to detect active cancer on RPLND. Additionally, the association between ctDNA levels and CS as a surrogate for disease volume was determined. Results: Sixty-four patients undergoing P-RPLND had pre-operative ctDNA collection with a median age of 37 (IQR:29-42). Plasma was collected on average, 8 days pre-operatively. Ten (16%) patients underwent P-RPLND for CS I and 54 (84%) for CS II disease. ctDNA was positive in 47 (73%) patients in the entire cohort. In the CS I cohort, 7 patients had a (-) ctDNA all of which had no disease on P-RPLND. Of the 54 patients in the CS II cohort, 44 (81%) had a (+) ctDNA. No false positives were found in this cohort. The SN, SP, PPV, and NPV in the CS I cohort were 100%, 78%, 33%, and 100% and in the CS II cohort were 88%, 100%, 100%, and 40%, respectively. Additionally, ctDNA level does not appear to correlate to disease volume at this juncture (r 2 =0, p=0.948). Conclusions: Circulating tumor DNA may have use in predicting retroperitoneal histology on P-RPLND. In CS I disease a negative test appears to be correlated with an absence of disease. In CS II disease, no false positives were found. ctDNA appears to be a binary test for detecting active disease in the retroperitoneum. Test statistics for circulating tumor DNA in detecting GCT for patients undergoing P-RPLND stratified by patients with CS I and CS II disease. CS 1 (N=10) Disease positive (n=1) Disease negative (n=9) + ctDNA (n=3) 1 2 PPV=33% - ctDNA (n=7) 0 7 NPV=100% SN=100% SP=78% CS 2 (N=54) n=50 n=4 + ctDNA (n=44) 44 0 PPV=100% - ctDNA (n=10) 6 4 NPV=40% SN=88% SP=100%