(P 047) FEASIBILITY OF A PERSONALIZED AND TUMOR-INFORMED CT-DNA ASSAY IN PATIENTS WITH LEIOMYOSARCOMA

Objective: Soft tissue sarcomas (STS) are aggressive rare tumors that make up ~1% of all malignant tumors. Leiomyosarcoma (LMS) is one of the most common STS subtypes, and patients are at high risk for metastatic relapse despite curative-intent surgery. Circulating tumor DNA (ctDNA) has emerged as a non-invasive biomarker that can detect molecular residual disease (MRD) post-surgery. The goal of this study was to evaluate the feasibility of performing ctDNA analysis to monitor patients with LMS and to assess disease progression and response to immunotherapy/surgery by correlating the findings with radiological imaging.

Methods: We retrospectively analyzed a cohort of 34 patients with LMS who had their corresponding samples run through Natera's CLIA lab. A total of 151 plasma samples were available for ctDNA analysis. The patients underwent treatment at the Stanford Sarcoma Program between September 2019 and May 2022. For ctDNA analysis, the patients were divided in two different cohorts; patients monitored in the adjuvant setting (N=15) and the metastatic setting (N=19). ctDNA analysis was performed using a personalized, tumor-informed ctDNA assay (Signatera, bespoke mPCR, NGS assay) and correlation with radiological imaging was assessed.

Results: A total of 34 patients with a mean age at diagnosis of 54 ± 10 (34 - 82) years [31 (91%) female] were included in this study. The median follow-up was 15.6 months (range: 4.4 - 80.8 months). In the adjuvant setting, 8/15 patients demonstrated recurrent disease. Of these, 6/8 patients were ctDNA-positive at one or more time points. In the metastatic setting, 15/19 patients demonstrated concordance between ctDNA results at the last plasma time point, and radiologic findings. In both these cohorts, 9 patients remained ctDNA-negative at the last plasma time point which corresponded with no evidence of disease on imaging at last follow-up.

Conclusion: Our study shows the feasibility of performing ctDNA testing in patients with LMS. The ctDNA status accurately correlated with radiographic imaging. In both adjuvant and metastatic settings, ctDNA status showed concordance with disease progression. Overall, our data suggests that ctDNA testing may be a viable approach in potentially reducing the frequency of radiologic imaging and sparing patients with unnecessary radiation exposure.