ctDNA as a predictor of outcome after curative resection for locally advanced rectal cancer: systematic review and meta-analysis

Aim: To assess the efficacy of ctDNA measurement at different time intervals in predicting response and prognosis in patients diagnosed with locally advanced rectal cancer (LARC) who underwent neoadjuvant treatment prior to curative resection. Method: English language randomized controlled trials and observational studies, published from 1946 to January 2024, comparing outcomes between ctDNA-positive and ctDNA-negative patients with LARC undergoing neoadjuvant treatment prior to curative surgical resection were included in the search. The search included Ovid MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and the Cochrane Database of Systematic Reviews (CDSR). Results: Data for 1022 patients were analysed. Patients with positive ctDNA in the preoperative period had more than five times the risk of developing distant metastasis (RR [95% CI] 5.03 [3.31-7.65], p < 0.001), while those with positive ctDNA in the postoperative period had more than six times the risk (RR [95% CI] 6.17 [2.38-15.95], p < 0.001). There was no significant relationship between ctDNA status at baseline, pre-, or postoperative periods and achievement of pCR (RR [95% CI] 1.21 [0.86-1.7], 1.82 [0.94-3.55], 1.48 [0.78-2.82], p = 0.27, 0.08, and 0.23, respectively). However, patients with positive ctDNA in the pre- and postoperative periods had more than 13 and 12 times the risk of overall disease relapse after curative-intent treatment (RR [95% CI] 13.55 [7.12-25.81], 12.14 [3.19-46.14], p < 0.001), respectively. Conclusion: ctDNA could potentially guide treatment and follow-up in LARC, predicting high-risk patients for disease relapse, allowing individualized surveillance and treatment strategies. Prospective studies are needed for standardization.