Abstract 1273: Predicting pathological response after ipilimumab plus nivolumab in stage III urothelial cancer by liquid-biopsy assessment of plasma and urine ctDNA using the RaDaR assay

Abstract Patients (pts) with stage III (cT3-4aN0M0 or cT1-4aN1-3M0) urothelial cancer (UC) have a poor prognosis. In NABUCCO cohort 1, 24 stage III UC pts were treated with ipilimumab (ipi) plus nivolumab (nivo) followed by radical surgery (day 1: ipi 3 mg/kg; day 22: ipi 3 mg/kg + nivo 1 mg/kg; day 43: nivo 3 mg/kg). 14/24 (58%) of pts showed a pathological response (ypT0N0 or ypTisN0/ypTaN0). Currently, there are no good biomarkers to assess response before surgery, potentially leading to overtreatment and unnecessary surgical complications. Here, we investigated whether detection of circulating tumor DNA (ctDNA) in plasma and urine by the RaDaR™ personalized liquid biopsy assay was associated with treatment response and outcomes. EDTA-plasma and urine supernatant were collected before start of treatment (day 1; “baseline”), before each subsequent treatment cycle (day 22 and 43) and before radical surgery. WES was performed on tumor FFPE and peripheral blood germline DNA to identify somatic variants for designing patient-specific, multiplex PCR-based NGS RaDaR™ panels. Plasma and urine ctDNA was analyzed using these panels to determine ctDNA detection and its estimated variant allele frequency (eVAF). Tissue somatic variants were detected in all patients, a median of 48 variants was used per RaDaR™ panel (range: 43-51). ctDNA was detected in 50/94 plasma samples (53%) and in 74/93 urine samples (80%). Detection levels were higher in urine with a median eVAF of 1.98% (range: 0.00057%-35.85%) vs. 0.049% (range: 0.00026%-18.94%) in plasma. ctDNA was detected in baseline plasma in 10/14 (71%) responding pts (median eVAF: 0.325%) and in 8/10 (80%) non-responders (median eVAF: 0.107%). Changes in ctDNA levels reflected clinical responses. After treatment with ipi plus nivo, ctDNA was undetectable in 13/14 (93%) responding pts, and in only 4/10 (40%) of non-responders (p=0.0088). Of the 17 pts with undetectable ctDNA before surgery, 13 (76%) had a pathological response and 16/17 (94%) pts remained recurrence-free after a median follow-up of 34 months. Urine ctDNA was detected at baseline in 12/14 (86%) responding pts (median eVAF: 9.634%) and in 8/10 (80%) non-responders (median eVAF: 2%). After treatment with ipi plus nivo, urine ctDNA was detected in 8/14 (57%) responding pts (median eVAF: 0.87%), and in 8/10 (80%) non-responders (median eVAF: 0.162%). No association was observed between urine ctDNA detection and response (p=0.39). Detection of plasma ctDNA by RaDaR™ after neoadjuvant treatment was associated with pathological response and clinical outcome. In contrast, ctDNA detection in urine was not associated with outcomes. Absence of plasma ctDNA pre-surgery may predict complete response to ipi plus nivo at surgery and may be helpful in guiding clinical decisions in stage III UC, in particular to select pts for bladder-sparing strategies. Citation Format: Jeroen van Dorp, Christodoulos Pipinikas, Nick van Dijk, Greg Jones, Alberto Gil-Jimenez, Giovanni Marsico, Maurits L. van Montfoort, Sophie Hackinger, Linde Braaf, Kirsten McLay, Daan van den Broek, Bas W. Van Rhijn, Nitzan Rosenfeld, Michiel S. van der Heijden. Predicting pathological response after ipilimumab plus nivolumab in stage III urothelial cancer by liquid-biopsy assessment of plasma and urine ctDNA using the RaDaR assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1273.