Circulating tumor DNA analysis in patients with esophageal cancer treated with neoadjuvant chemoradiotherapy followed by surgery.

69 Background: The aim of this prospectively study is to investigate circulating tumor DNA (ctDNA) as a prognostic marker for survival in locally advanced esophageal squamous cell cancer (ESCC) patients treated with neoadjuvant chemoradiotherapy (nCRT) and surgery. Methods: Serial plasma samples were collected from 68 ESCC patients treated with neoadjuvant chemoradiotherapy before surgery. ctDNA was detected before treatment, after neoadjuvant chemoradiotherapy and after surgery by personalized, next-generation sequencing assay. Cox regression analyses were used to evaluate the prognostic significance of ctDNA for recurrence-free survival (RFS) and overall survival (OS). Results: ctDNA was detectable in 89.7%, 17.2%, and 6.9% of pretreatment, post-neoadjuvant chemoradiotherapy and post-surgery plasma samples, respectively. The conversion of ctDNA status from positive at baseline to negative at 4-6 weeks after neoadjuvant chemoradiotherapy was significantly associated with pathological complete response (pCR) ( P = 0.02). Significant worse RFS was related to detectable ctDNA after neoadjuvant chemoradiotherapy ( P = 0.008) or after surgery ( P = 0.001). Detectable ctDNA at baseline ( P = 0.01) and after surgery ( P = 0.008) were associated with worse OS. In multivariate analysis, detectable postoperative ctDNA was significantly associated with RFS ( P = 0.012) and OS ( P = 0.025) after adjusting for other clinicopathological risk factors. Conclusions: ctDNA status is a strong prognostic factor of recurrence in locally advanced ESCC patients. Consequently, ctDNA could potentially improve pre- and post-treatment risk assessment and facilitate individual therapy for ESCC patients.