EP217 - Identifying Mismatch Repair Deficient Colon Cancer Appropriate for Neoadjuvant Immunotherapy

Sunday, May 10, 2026

8:43 AM - 8:48 AM ET

ePoster Presenter(s)

Matthew B. Hill, MD

Research Fellow
Memorial Sloan Kettering Cancer Center
Memorial Sloan Kettering Cancer Center
New York, NY, United States

Disclosure information not submitted.

Author(s)

JF

James L. Fuqua, MD

Assistant Professor, Radiology
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
Andrea Cercek, MD

Associate Physician
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
NS

Neil H. Segal, MD PhD

Attending, Medical Oncology
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
LS

Leonard Saltz, MD

Attending Physician
Department of Medical Oncology, Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
Julio Garcia Aguilar

Disclosure information not submitted.
MG

Mithat Gonen, PhD

Attending Biostatistician
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.

Senior Author(s)

Martin R. Weiser, MD

Vice Chair for Faculty Affairs
Memorial Sloan Kettering Cancer Center
Cornell Medical College
New York, New York, United States

Disclosure information not submitted.

Purpose/Background: Neoadjuvant immunotherapy has been proposed as initial treatment for mismatch repair deficient (MMR-D) colon cancer to downstage disease and avoid adjuvant cytotoxic chemotherapy. Concern has been expressed that Computed Tomography (CT) scan will overestimate node positivity and T stage due to robust immune reaction to MMR-D tumors.

Methods/Interventions: We queried a prospectively maintained, IRB-approved, institutional database for patients with MMR-D colon cancer who did not receive neoadjuvant therapy and who underwent colectomy between 2019-2024. Preoperative CT scans reviewed by a dedicated GI radiologist identified clinical T4 and/or node positive (N+) disease. N+ disease was defined as at least 1 lymph node (LN) ≥ 1 cm. Univariate and multivariate analyses were performed to identify preoperative risk factors which could predict T4 or N+ disease that might benefit from neoadjuvant immunotherapy.

Results/Outcomes: A total of 245 patients with MMR-D colon adenocarcinoma, 148 (60%) female, with a median age of 71 years (IQR 57-77), were included. Tumors were located in the ascending colon (122; 50%), cecum (58; 24%), transverse colon (34; 14%), descending colon (19; 7.8%), and rectosigmoid (12; 4.9%). Clinical staging via CT scan determined 25 tumors (10%) were T4 and 37 (15%) were N+. Surgical resection included right colectomy (189; 77%), transverse colectomy (9; 3.7%), left colectomy (23; 9.4%), sigmoid colectomy (4; 1.6%), LAR (6; 2.4%), subtotal colectomy (3; 1.2%), and total colectomy (11; 4.5%). Final AJCC staging: stage 1 (77; 31%), stage 2 (105; 43%), and stage 3 (63; 26%). Based on pathologic staging, 24 (9.8%) of tumors were T4 and 63 (26%) were N+. The most common MMR protein loss was MLH1 / PMS2 (190; 78%) followed by MSH2 / MSH6 (29; 12%) and 57 (23%) had Lynch Syndrome. On multivariate analysis tumor location, tumor infiltrating lymphocytes (TILs), MMR protein loss, and Lynch Syndrome were not predictive of either node-positive or T4 disease. Positive-predictive value of CT staging for T4 and N+ disease were 64% and 70% while negative-predictive value were 96% and 82% for T4 and N+ disease, respectively.

Conclusion/Discussion: Contrary to expectations, CT scan primarily underestimates N+ disease and CT scan alone may not be sufficient to identify high risk stage II or stage III MMR-D colon cancer. Novel markers are needed to more accurately identify T4 and N+ disease to fully realize the benefit of neoadjuvant immunotherapy in MMR-D colon cancer.