Correlation of circulating tumor DNA (ctDNA) with clinical outcomes in appendiceal cancers (AC).

29 Background: Appendiceal Cancers are a heterogenous group of rare tumors with distinct histopathologic and genomic alterations. These often have peritoneal spread that might not be easily detected on current imaging modalities, and conventional tumor markers may not lend diagnostic support. Hence, novel diagnostic techniques are needed. Measurement of ctDNA for recurrence risk prediction, response to therapy and and early diagnosis is a promising technique. However, limited published data exist in AC to validate the role and utility of ctDNA in clinical practice. Here we present a single institution experience of ctDNA analysis in patients with AC. Methods: ctDNA measurements of 37 pts with stage II-IV AC treated between 1/1/2019 and 9/15/2021 were reviewed retrospectively. ctDNA analysis was done using Signatera bespoke mPCR NGS assay. ctDNA results were compared to crossectional imaging, CEA levels, and clinical evaluation. Results: 19/37 patients (51%) had at least one positive ctDNA test result. Of those, 8 had testing done during the surveillance setting (two with grade 3, one with grade 2, two with grade 1, and three with unknown grade). Of those, 5 pts (62.5%) had positive ctDNA detected, while 33.33% had elevated CEA level, 25% had radiographic and 42.9% had clinical evidence of recurrence (Table). 7/14 (50%) pts had high-grade pathology and positive ct-DNA, 3/6 (50%) patients had low-grade (grade 1) pathology and positive ct-DNA findings. 4 patients had longitudinal ct-DNA measurements available which correlated well with their disease course. Median duration to recurrence (radiographic or laparoscopic) was 376 days. Median duration to the first positive ctDNA test was 370 days. Median duration to positive CEA after initial treatment was 475 days. Conclusions: Measurement of ctDNA can be a useful tool to follow disease course and to guide management decision-making in patients with AC. Prospective studies with serial measurements of ctDNA are planned. [Table: see text]