eP825 - Liquid biopsy Epigenetic Markers to Assess Therapeutic Inertia for Augmented Safety and Enhanced Organ Preservation in Locally Advanced Rectal Cancer.

Image or Table (Do Not add text here): Visual Abstract

Purpose/Background: Liquid biopsies utilizing epigenetic methods, particularly Septin 9 methylation analysis, have shown promising correlations with tumor burden due to the link between DNA methylation changes and the number of affected cells.
This study aims to quantify actual tumor burden in patients with colorectal cancer and assess treatment response and potential inertia using Septin 9 methylation analysis in liquid biopsies.
OBJECTIVE 1: This information is crucial for extending the observation period after a non-complete response.
OBJETIVE 2: Conversely, in cases of early excellent local responses to neoadjuvant treatment, the consideration of avoiding TNT becomes pertinent.Methods/Interventions: Prospective Observational Study.

Patient selection criteria: Locally advanced middle or low rectal cancer. Exclusion criteria: Metastatic disease.

Intervention: This study adheres to the treatment guidelines for rectal cancer established by the National Comprehensive Cancer Network (NCCN). The protocol, named Forest, has received approval from the Jiménez Díaz Foundation Hospital Ethics Committee. Septin 9 methylation will be monitored throughout the study.

Septin 9 methylation will be quantitatively analyzed using droplet digital PCR (BIORAD). This ratio is determined by the count of positive droplets observed for methylated and unmethylated targets during fluorescence analysis. Elevated Septin 9 methylation ratios typically signify heightened methylation of the Septin 9 gene, commonly linked with active disease states.

BASELINE Septin 9 methylation level in blood sample will be measured at diagnosis, and will follow the treatment schedule below:

Weeks 1-4 Neoadjuvancy: Long-cycle Radiotherapy + neoadjuvant chemotherapy.
Weeks 4-6 Therapeutic Inertia Time: Consolidation with FOLFOX.

A SECOND Septin 9 methylation assessment will be performed at weeks 4-6: If a complete clinical response is obtained consolidation with FOLFOX will be avoided

Weeks 20-26 Decision: Evaluation of response by the tumor committee. Possible scenarios and treatment strategies are as follows:
• Complete clinical response: Watch and Wait follow-up.
• Almost complete clinical response: A THIRD Septin 9 methylation assessment: High Septine rate will indicate local excision and PET TC. Low Septine methylation rate will extend the observation peridod.
• Incomplete response: Radical rectal resection.

A two-year follow-up period will be conducted with a particular emphasis on meticulously documenting both oncological and surgical adverse events.

SAMPLE SIZE

The sample size has been calculated to estimate sensitivity and specificity values with a certain level of precision, based on the width of the 95% confidence interval. Assuming sensitivity and specificity around 80% and aiming for a precision of 12%, 40 patients who are true negatives and 40 patients who are true positives will be needed. It is expected that approximately 40% of the included patients will be true negatives. Given these considerations, at least 110 patients need to be included in the study.Results/Outcomes: PendingConclusion/

Discussion: Epigenetic Tools that may quantify tumor burden or, ideally, determine treatment inertia to discern tumor progression or regression are interesting tools for treatment decision-making.
In this prospective observational study, we will investigate the utility of the Septin 9 methylation ratio, a readily accessible epigenetic marker, to assess its effectiveness in this contextVisual Abstract