Abstract
BACKGROUND AND OBJECTIVES: Circulating tumor DNA (ctDNA) can potentially identify rectal cancer patients benefiting from neoadjuvant and adjuvant therapy. This study compared droplet digital PCR (ddPCR) and next-generation sequencing (NGS) for ctDNA detection in localized rectal cancer before and after surgery. METHODS: Pre-therapy plasma and rectal tumor samples were collected from a development group (n = 41) and a validation group (n = 26). Mutations in tumor samples were identified using NGS, and ctDNA detection was performed with both ddPCR and NGS. Recurrence was assessed 1 year after surgery in the development group. RESULTS: In the development group, ddPCR detected ctDNA in 24/41 (58.5%) and NGS panel in 15/41 (36.6%; p = 0.00075) of the baseline plasma. In the validation group, 21/26 (80.8%) patients had detectable ctDNA in the pre-therapy plasma. A positive ctDNA result was associated with higher clinical tumor stage and with lymph node positivity as detected by MRI. Postoperative ddPCR did not detect ctDNA before most recurrences. CONCLUSIONS: We demonstrated a practical oligomarker ctDNA test for localized rectal cancer suitable for clinical workflow, and that ddPCR detects ctNA from pre-therapy plasma at a satisfactory level in advanced rectal cancers. Detecting ctDNA with ddPCR may help to assess the local severity, but the clinical utility of this approach should be evaluated in clinical trials.