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Session: ePoster: Rectal Cancer 2 (Sun1230)

EP457 - ctDNA to detect minimal residual disease in patients with locally advanced rectal cancer after total neoadjuvant therapy

Sunday, May 11, 2025
12:40 PM – 12:45 PM PT
Location: Monitor 9, Sails Pavilion, Upper Level

    ePoster Presenter(s)

  • Jin K. Kim, MD

    Colorectal Surgery Fellow
    University of South Florida
    Tampa, FL, United States

    All of the relevant financial relationships listed below have been mitigated.
    This individual has no financial relationships with ineligible companies.

    • Senior Author(s)

  • JM

    Jorge Marcet, MD

    Director, Division of Colon and Rectal Surgery
    USF Morsani College of Medicine
    Tampa, Florida, United States

    Disclosure information not submitted.

    • Author(s)

  • RB

    Robert D. Bennett, FACS, FASCRS

    Associate Professor of Surgery
    University of South Florida Morsani College of Medicine
    Tampa, Florida, United States

    All of the relevant financial relationships listed below have been mitigated.
    This individual has no financial relationships with ineligible companies.

  • CM

    Carolina Martinez, MD

    Assistant Professor
    University of South Florida
    Tampa, Florida, United States

    Disclosure information not submitted.

All of the relevant financial relationships listed below have been mitigated.
Jin K. Kim, MD: This individual has no financial relationships with ineligible companies.
Robert D. Bennett, FACS, FASCRS: This individual has no financial relationships with ineligible companies.
Image or Table (Do Not add text here):

Purpose/Background: “Watch and wait” nonoperative management of patients with locally advanced rectal cancer (LARC) who respond well to total neoadjuvant therapy (TNT) has been shown to be oncologically safe. Nonoperative management (NOM) also benefits patients by avoiding the morbidity associated with total mesorectal excision. However, identifying responders to TNT that may benefit from NOM is clinically challenging. ctDNA testing has shown promise in detecting minimal disease in several cancers but has not yet been studied within this clinical context. In this case series, we studied whether ctDNA testing after TNT can help detect minimal residual disease in the rectum.

Methods/Interventions: This is a single institution retrospective case series study of LARC patients treated with TNT from 2019-2023 who underwent ctDNA testing as an adjunct to the standard serial clinical response assessments. Total neoadjuvant therapy was defined as preoperative radiotherapy plus fluorouracil based systemic chemotherapy. Standard serial clinical response assessment consisted of pelvic MRI, CT chest/abdomen/pelvis, digital rectal exam, and flexible sigmoidoscopy at 3-6 month intervals. Tumor-informed ctDNA testing was performed with Signatera (Natera Inc, San Carlos, CA, USA) which utilizes patient-specific tumor mutations to perform next-generation sequencing of plasma cell-free DNA.

Results/Outcomes: A total of 26 LARC patients had ctDNA testing as part of their response assessment after TNT. 3 patients had positive ctDNA and 23 patients had negative ctDNA after completion of TNT. Baseline characteristics of these two groups are listed in Table 1. None of the patients had signs of distant metastasis at response assessment. All patients who had a positive ctDNA underwent surgery and had residual rectal cancer in the specimen. 5 of 23 patients who had a negative ctDNA underwent surgery. Only 4 (17% of the 23 patients) had residual rectal cancer in this group.

Conclusion/Discussion: ctDNA testing has the potential to detect minimal residual disease in LARC patients treated with total neoadjuvant therapy. A prospective clinical trial may help better define the utility of ctDNA testing as part of response assessment to identify candidates that may benefit from watch and wait.