ctDNA analysis of rectal cancer treated in the watchful waiting setting

Watchful waiting is a new concept in the treatment of rectal cancer implying observation after chemoradiation without surgery. Patients in clinical complete remission after chemoradiation are offered observation instead for operation. Our previous studies indicated that more than half of this patient group could be spared mutilating surgery with low toxicity and high quality of life. The present study is a national multicenter trial, which enrolled 105 patients.

The primary endpoint is the fraction of patients with locoregional tumor control two years after end of treatment. Secondary endpoints are rate distant metastases, toxicity, quality of life, and overall survival. The rate of local recurrence is expected to be around 25%, but according to our previous results almost all recurring patients can be offered curatively intended surgery. At present, the major issue is selection of patients for surgery or observation after chemoradiation.

The present study aims to investigate if ctDNA can be used as an objective tool for this purpose. A further perspective is the possible relationship between ctDNA status and distant metastases as investigated by serial measurement. Blood samples have been collected before chemoradiation, at the end of treatment and at every follow-up visit allowing for serial analysis of ctDNA. All samples are at hand at the participating departments.

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PhD student Edina Dizdarevic

Department of oncology, Vejle Sygehus