Circulating tumor DNA (ctDNA) as a marker of recurrence risk in stage II colon cancer (CC).

Abstract

11015 Background: Markers that better define recurrence risk for patients (pts) with stage II CC are urgently required, potentially defining a subset that would most benefit from adjuvant chemotherapy (CTX) and intensive surveillance. An alternative strategy to standard analyses of the resected surgical specimen is to directly examine plasma for evidence of residual disease. Recently, ctDNA has shown promise as a blood biomarker in advanced colorectal cancer; here we explore the potential of this marker in stage II CC. Methods: In this prospective study, plasma samples are being collected at 4-10 weeks post-op in 250 stage II CC pts, with serial 3 monthly samples on a subset of 175 pts. Adjuvant CTX is at clinician discretion, blinded to ctDNA analysis. Surveillance includes 3 monthly CEA and 6 monthly CT imaging for 2 years. All samples were sent to Johns Hopkins Kimmel Cancer Center, where tumor tissue was analyzed for hotspot mutations in TP53, APC, KRAS, NRAS, BRAF, PIK3CA, CTNNB1, SMAD4, and FBXW7 us...