Whole-genome sequencing–based ctDNA testing for post-surgical monitoring and early detection of recurrence or progression in uterine cancer.

5623 Background: Reliance on clinicopathologic risk factors to guide adjuvant therapy in early-stage uterine cancer (UC) has not improved survival, underscoring the need for biomarkers for post-treatment monitoring. In this study, we evaluate ctDNA as a prognostic biomarker using a whole-genome sequencing (WGS)–based assay in the post-surgical UC setting. Methods: We performed a retrospective analysis of clinically annotated residual samples from commercial ctDNA testing in 118 patients diagnosed with UC. Signatera Genome assays (Natera, Inc.) were designed from the WGS data of matched tumor tissue and normal blood samples to detect and quantify ctDNA in serially collected post-operative plasma. Descriptive statistics were used to compare association of ctDNA across stages and timepoints. Results: Among 118 UC patients, 20/118 were metastatic and excluded from analysis. Of the remaining 98 patients, 77 had stage I and 21 had stage II-III disease. Median clinical follow-up was 11.2 months (range: 0.8–33.2) with 13% (13/98) of patients having recurrence/progression within a median of 8.5 (range: 3.9-25.1) months from surgery. ctDNA analysis was performed across 1004 total tests with a median of 8 tests per patient (range: 2–16) and a median testing cadence of 2.9 (range: 0-12.7) months. Post-surgical ctDNA assessment (2–8 weeks post-operatively) was available for 35 stage I patients with a ctDNA detection rate of 9% (3/35). Focusing on the 32 patients with >12 months of postoperative clinical follow-up, one patient was ctDNA-positive postoperatively and recurred 7.2 months after surgery. Among the ctDNA-negative patients (N=31), 84% (26/31) remained serially negative with no evidence of recurrence at a median clinical follow-up of 26.3 (range: 13.5-38.7) months post-surgery. The remaining ctDNA-negative patients (N=5) converted to positive during longitudinal monitoring, all subsequently experiencing recurrence/death. Longitudinal ctDNA detection rate during surveillance was 32.1% (25/78) in stage I and 47.6% (10/21) in stage II-III. Of the stage I patients with recurrence (N=8), 100% were ctDNA-positive prior to or at the time of the clinical finding, with a median lead time of 5.2 (range: 1.2–15.8) months. Similarly, in stage II-III patients with recurrence/progression (N=5), 100% were ctDNA-positive prior to the clinical finding with a median lead-time of 6.07 (range: 4.1-23.7) months. Conclusions: ctDNA positivity postoperatively identifies UC patients at increased risk of recurrence/progression, often preceding clinical relapse by several months. Serial ctDNA negativity using a tumor-informed, WGS-based ctDNA assay correlated with absence of recurrence. Postoperative longitudinal ctDNA monitoring shows promise as a clinically actionable biomarker to guide adjuvant treatment decisions and improve post-operative surveillance.