Utility of circulating tumour DNA for prognosis and prediction of therapeutic effect in locally recurrent rectal cancer: study protocol for a multi-institutional, prospective observational study (JCOG1801A1, CAP-LR study).

The study protocol received approval from the Institutional Review Board of National Cancer Center Hospital East on behalf of the participating institutions in February 2023. The study is conducted in accordance with the precepts established in the Declaration of Helsinki and Ethical Guidelines for Medical and Biological Research Involving Human Subjects. Written informed consent will be obtained from all eligible patients prior to registration.