Use of molecular residual disease (MRD) testing with measurement of circulating tumor DNA (ctDNA) post-operatively in stage II colon cancer (SIICC) in the community-based setting.

53 Background: 80% of adult oncology patients (pts) are treated in the community-based setting. Data on the implementation of emerging technologies such as ctDNA testing is scant in this population. Use of adjuvant chemotherapy in SIICC pts historically was based on clinical/pathological risk factors however new data presented in mid 2022 utilizes the presence or absence of ctDNA 6-8 weeks post operatively to help risk stratify pts. The absence of ctDNA predicts a high chance of disease-free survival. Use of ctDNA was incorporated into the NCCN Colon Cancer guidelines as of 2023. In a private practice setting, we retrospectively looked at the use of ctDNA assay for adjuvant chemotherapy decision-making in SIICC pts. Methods: We conducted a retrospective study to quantify ctDNA testing frequency in SIICC pts in our community based oncology practice. The historical cohort was comprised of pts diagnosed prior to the NCCN guideline inclusion of ctDNA; the current cohort included pts diagnosed after the NCCN guideline change. For all pts, we reviewed clinicopathologic risk factors deemed to be high risk (positive margin, < 12 LN removed, tumor budding, lymphovascular invasion, poorly differentiated features; perforation or obstruction) and used this for stratification. Low-risk pts had no high risk features. Medical record data (office notes, pathology, molecular testing) was evaluated to determine ctDNA results including timing and use of adjuvant chemotherapy. Primary endpoint was the percent (%) of current pts who were low-risk with ctDNA testing sent compared to historical control. Secondary endpoint was the % of ctDNA testing sent within 8 weeks of curative surgery in both cohorts. Results: In a private practice setting, we identified low-risk SIICC pts spanning a 36-month period and categorized them into two groups: the historic cohort (A) pts were diagnosed between July 2021-Dec 2022, and the active cohort (B) pts were diagnosed between Jan 2023-July 2024. 26 pts were identified in cohort A and 36 pts were identified in cohort B to have SIICC. Out of 26 pts in cohort A, we identified 13 low risk SIICC pts; for cohort B, out of 36 pts, we identified 25 low-risk SIICC pts. The percentage of pts in each group that had ctDNA testing sent was 79.6% (10/13 pts) in cohort A and 92% (23/25 pts) in cohort B. In cohort A, 80% (8/10 pts) and in cohort B, 90.9% (20/22 pts) had ctDNA sent within 8 weeks of surgery. Conclusions: Incorporation of ctDNA testing in low-risk SIICC pts in a community-based setting occurred quickly. As ctDNA testing was implemented into practice, a majority of pts had the testing sent in the appropriate time frame. Future best practices, especially in the community, should incorporate tumor specific clinician oversight with use of updated pathways to ensure any recent changes to standard of care are followed.