A Prospective Feasibility Study Evaluating Extracellular Vesicles Obtained by Liquid Biopsy for Neoadjuvant Treatment Response Assessment in Rectal Cancer

Routine clinical and radiological assessment of response of patients with rectum cancer to neoadjuvant chemoradiotherapy does not allow accurate identification of complete pathological response, and leads to frequent false positive and negative results. Molecular markers reflecting the initial and post-nCRT status of the tumor would be ideal to select patients eligible for organ preservation. This project will test the detection of tumor extracellular vesicles (EVs) in liquid biopsy as a reliable marker for the identification of poor versus good responders to nCRT.

Neoadjuvant treatment (NT) followed by total mesorectum excision (TME) constitues the gold standard for locally advanced carcinoma of the low and middle rectum. When good clinical response to NT is obtain, strategies with organ preservation, including close surveillance without immediate surgery or transanal local excision, can spare patients with the highly morbid and functional cost of TME. Current assessment of good responders relies on the downstaging and/or downsizing of the tumor as evaluated by MRI imaging and clinical exam. This strategy is prone to errors in more than 1/3 cases. Better assessment of tumor response to NT would better select patients eligible for organ preservation strategies. This study will use the detection of tumor extracellular vesicles (EVs) in liquid biopsy to identify good response of rectum cancer to neoadjuvant treatment. Tumor EVs will be detected in the blood of the patients at different times of their regular management (before, during and after NT). Protein content or tumor DNA in EVs will be detected after tumor DNA sequencing in the primary biopsies. Response will be assessed according to tumor EV presence or absence in the blood. As EV quantification is possible, kinetics of their detection will help response assessment and patient follow-up.