Purpose: We investigated the value of circulating tumor DNA (ctDNA) in predicting tumor response to neoadjuvant chemoradiotherapy (nCRT), monitoring tumor burden, and prognosing survival in patients with locally advanced rectal cancer (LARC). Experimental Design: This prospective multicenter trial recruited 106 LARC patients for treatment of nCRT followed by surgery. Serial ctDNA were analyzed by NGS at four time points: at baseline, during nCRT, pre-surgery and post-surgery. Results: In total, 1098 mutations were identified in tumor tissues of the 104 patients being analyzed (median, 7 mutations per patient). ctDNA was detected in 75%, 15.6%, 10.5%, and 6.7% of cases at the four time points, respectively. None of the 29 patients with pathological complete response (ypCR) had preoperative ctDNA detected. Preoperative ctDNA positive rate was significantly lower in the well responded patients with pathological tumor regression grade of ypCAP 0-1 than ypCAP 2-3 group (P < 0.001), lower in ypCR than non-ypCR group (P = 0.02), and lower in ypT 0-2 than ypT 3-4 group (P = 0.002). With a median follow-up of 18.8 months, thirteen patients (12.5%) experienced distant metastasis. ctDNA positivity at all four time points was associated with a shorter metastasis-free survival (MFS) (P < 0.05). Multivariate analyses showed that the median VAF of mutations in baseline ctDNA was a strong independent predictor of MFS (HR=1.27, P < 0.001). Conclusions: We show that ctDNA is a real-time monitoring indicator that can accurately reflect the tumor burden. The median VAF of baseline ctDNA is a strong independent predictor of MFS.

PURPOSE: Complete mesocolic excision (CME) is being increasingly used for the treatment of right-sided colon cancer, although there is still no strong evidence that CME provides better long-term oncological outcomes than D2 dissection. The controversy is mainly regarding the survival benefit from extended lymph node dissection emphasized by CME. METHODS: This multicenter, open-label, randomized controlled trial (ClinicalTrials.gov identifier: NCT02619942 ) was performed across 17 hospitals in China. Patients diagnosed with stage T2-T4aNanyM0 or TanyN + M0 right-sided colon cancer were randomly assigned (1:1) to undergo either CME or D2 dissection during laparoscopic right colectomy. The primary outcome was the 3-year disease-free survival (DFS), and the main secondary outcome was the 3-year overall survival (OS). RESULTS: Between January 11, 2016, and December 26, 2019, 1,072 patients were randomly assigned (536 patients to CME and 536 patients to D2 dissection). In total, 995 patients (median age 61 years, 59% male) were included in the primary analysis (CME [n = 495] v D2 dissection [n = 500]). No significant differences were found between the groups in 3-year DFS (hazard ratio [HR], 0.74 [95% CI, 0.54 to 1.02]; P = .06; 86.1% in the CME group v 81.9% in the D2 group) or in 3-year OS (HR, 0.70 [95% CI, 0.43 to 1.16]; P = .17; 94.7% in the CME group v 92.6% in the D2 group). CONCLUSION: This trial failed to find evidence of superior DFS outcome for CME compared with standard D2 lymph node dissection in primary surgical excision of right-sided colon cancer. Standard D2 dissection should be the routine procedure for these patients. CME should only be considered in patients with obvious mesocolic lymph node involvement.

The extent of lymphadenectomy during laparoscopic right colectomy can affect the oncological outcome and the safety of surgery. The principle of complete mesocolic excision (CME) has been gradually accepted and increasingly applied by colorectal surgeons. The aim of this study is to investigate whether extended lymphadenectomy (CME) in laparoscopic colectomy could improve the oncological outcomes of patients with right-sided colon cancers, compared with D2 lymphadenectomy. The Radical Extent of lympadenectomy: D2 dissection versus complete mesocolic excision of LAparoscopic Right Colectomy for right-sided colon cancer (RELARC) study is a prospective, multicenter, randomized controlled trial in which 1072 eligible patients with right-sided colon cancers will be randomly assigned to the CME group or the D2 dissection group during laparoscopic right colectomy. Inclusion criteria are locally advanced colon cancers situated from the cecum to the right third of the transverse colon and clinically staged as T2-4aN0M0 or TanyN + M0. The primary endpoint of this trial is 3-year disease-free survival. Secondary endpoints include 3-year overall survival, postoperative complication rates, perioperative mortality rates, and rates of positive central lymph nodes (the station 3 nodes). The RELARC trial is a prospective, multicenter, randomized controlled trial that will provide evidence on the optimal extent of lymphadenectomy during laparoscopic right colectomy in terms of better oncological outcome and operation safety. ClinicalTrials.gov: NCT02619942 . Registered on 29 November 2015.