Monitoring Treatment Response in Rectal Cancer through Circulating Tumor Cell Dynamics: A Pilot Clinical Study.

Background: Circulating tumor cells (CTCs) are increasingly recognized as a minimally invasive biomarker with significant potential in oncologic monitoring and prognostication. This study aimed to assess the dynamics of CTC levels in patients with rectal cancer undergoing multimodal treatment and evaluate their potential role in therapeutic decision-making.

Methods: We conducted a prospective, observational study of 56 patients with histologically confirmed rectal adenocarcinoma. Patients underwent either primary surgical resection or neoadjuvant chemoradiotherapy (CRT) followed by surgery. Peripheral blood samples were collected at defined intervals and analyzed using the CytoTrack CT11™ system to detect and quantify CTCs.

Results: Pretreatment CTCs were detected in 16.1% of patients. In the primary surgery group, all preoperatively positive CTC cases became negative postoperatively, although transient positivity was observed in two cases at 1 week post-surgery. In the CRT group, 35.7% of patients exhibited detectable CTCs during treatment, with complete clearance after surgery. The dynamic change in CTC levels correlated with therapeutic response and potential recurrence risk.

Conclusions: This pilot study highlights the clinical relevance of CTC monitoring in rectal cancer. CTC dynamics appear to reflect treatment efficacy and may serve as an early indicator of response. These findings support the development of a randomized clinical trial comparing rectal cancer treatments with and without neoadjuvant therapy, using CTC trends as a primary outcome measure.