EP671 - Diagnosis of clinical complete response in mucinous rectal cancer

Monday, May 12, 2025

8:10 AM – 8:15 AM PT

Location: Monitor 10, Sails Pavilion, Upper Level

ePoster Presenter(s)

SN

Sowmya Narayanan, MD, PhD

Colorectal surgery fellow
Cleveland Clinic
Cleveland, OH, United States

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

Author(s)

Salih Karahan, MD

Research Fellow
Cleveland Clinic Department of Colorectal Surgery
Cleveland Heights, Ohio, United States

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This individual has no financial relationships with ineligible companies.
JS

Josh Sommovilla, MD

Assistant Professor of Surgery
Cleveland Clinic
Cleveland, Ohio, United States

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

Arielle E. Kanters, MD, MS

Colorectal Surgeoin
Cleveland Clinic
Cleveland, Ohio, United States

Disclosure information not submitted.
Michael A. Valente, DO

Associate Professor of Surgery
Cleveland Clinic
cleveland, Ohio, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.
David R. Rosen, MD

Colorectal Surgeon
Cleveland Clinic
Cleveland Clinic Lerner College of Medicine
Cleveland, Ohio, United States

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

Emre Gorgun, MD, MBA

Vice Chair, Department of Colorectal Surgery
Cleveland Clinic Foundation-Main Campus
Cleveland, Ohio, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no relevant relationships with ineligible companies.
Scott R. Steele, MD, MBA

President, Cleveland Clinic, Main Campus Submarket and Rupert B. Turnbull M.D., Endowed Chair in Colorectal Surgery
Cleveland Clinic
Cleveland, OH, United States

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This individual has no financial relationships with ineligible companies.

Senior Author(s)

David Liska, MD

Associate Professor, Chair
Department of Colorectal Surgery, Cleveland Clinic
Cleveland Clinic, Cleveland, Ohio
Cleveland, Ohio, United States

Disclosure information not submitted.

All of the relevant financial relationships listed below have been mitigated.

Sowmya Narayanan, MD, PhD: This individual has no financial relationships with ineligible companies.

Salih Karahan, MD: This individual has no financial relationships with ineligible companies.

Josh Sommovilla, MD: This individual has no financial relationships with ineligible companies.

Michael A. Valente, DO: This individual has no financial relationships with ineligible companies.

David R. Rosen, MD: This individual has no relevant relationships with ineligible companies.

Emre Gorgun, MD, MBA: This individual has no relevant relationships with ineligible companies.

Scott R. Steele, MD, MBA: This individual has no financial relationships with ineligible companies.

Image or Table (Do Not add text here):

Purpose/Background: Rectal mucinous adenocarcinoma (RMA) has a poor prognosis and is less responsive to chemoradiation when compared to non-mucinous tumors. The impact of total neoadjuvant therapy (TNT) in this subset of patients is still unclear and current imaging techniques cannot distinguish between cellular and acellular mucin. We hypothesized that clinical complete response (cCR) is rarely found in patients with RMA following TNT.

Methods/Interventions: This retrospective study included 39 patients with clinical stage II/III mucinous rectal cancer treated with TNT at our quaternary referral center from 2018-2023. RMA patients were identified by the radiographic presence of extracellular mucin (T2-hyperintense signal) on initial staging MRI. Demographics, tumor and treatment characteristics, and treatment response were assessed. Complete response (CR) was defined as patients with sustained clinical response > 1 year or pathological complete response (pCR); clinical complete response (cCR) was defined as no evidence of residual tumor on digital rectal examination and endoscopy, and MRI tumor regression grade (mrTRG) of 1-2. Concordance between clinical response and assessment methods were calculated using the weighted kappa test.

Results/Outcomes: Our cohort of 39 RMA patients included 25 (64.1%) males, the majority of whom were White (34, 87.2%) with an average age of 59.5 ± 9.4 years. The tumors were locally advanced cancers (stage II 10, 25.6%; stage III 29, 74.3%) treated with long-course chemoradiation (38, 97.4%) followed by consolidation chemotherapy (37, 94.9%). Only 2 patients (5.1%) had a cCR at a median of 4.6 (IQR 3.4-6) weeks after finishing TNT; 4 were followed with our watch and wait protocol (2 cCR and 2 with near-cCR), 3 of whom maintained organ preservation. On pathological assessment of the 36 patients who underwent resection, 8 (20.5%) had a pCR or TRG 0. Only 3 of the 11 patients with CR had an mrTRG 1-2 indicative of cCR. When compared to endoscopy, MRI had lower sensitivity, but comparable specificity for predicting CR (Table 1).

Conclusion/Discussion: Patients with RMA had lower rates of organ preservation and clinical and pathological CR following TNT when compared to established trends in non-mucinous rectal adenocarcinomas. There was also low sensitivity in clinically detecting a complete response following TNT, driven especially by the presence of acellular mucin that can be indistinguishable from lack of treatment response on MRI. These results suggest that RMA patients may require different diagnostic modalities to accurately detect CR and derive the benefit of organ preservation from TNT.