825 Assessment of a circulating tumor DNA test for detecting recurrence of Merkel cell carcinoma

Approximately 40% of patients with Merkel cell carcinoma (MCC) develop recurrence or metastasis. Early detection can result in better outcomes, and effective surveillance is critical MCC management. We assessed whether circulating tumor DNA (ctDNA) accurately detect clinically evident and/or occult MCC. used the SignateraTM platform which tumor-specific mutations are identified from archival tumors, blood interrogated for those mutations. Since April 2020, we have collected longitudinal ctDNA samples 95 patients. Of these, 38 had 57 did not. MCC, all a positive test (sensitivity: 100%, 95% CI: 91-100%). Among these 38, 20 were newly diagnosed The median size cases was 2.5 cm (range 1-8.5), 30 mean molecules/mL 0.08-1470). Primary value strongly correlated (Spearman’s r = 0.74, p < 0.001). without clinical evidence disease, 49 negative test. Eight current disease. Four 8 developed recurrent at 55-217 days later. specificity subsequently 92% (95% 82-98%). remaining 4 test, 2 independent early disease based on marked elevation polyomavirus oncoprotein antibody titers (an established half who produce such antibodies). conclude that quantitation may be more sensitive than imaging to minimal residual this perform well regardless viral status.