EP210-2 - Chemotherapy vs Chemoimmunotherapy in the Treatment of Metastatic Microsatellite Instability-High (MSI-H) Colorectal Cancer: A National Cancer Database

ePoster Presenter(s)

• 

  George L. Wu, B.S.

  Research Assistant
  Surgery Group of Los Angeles
  Los Angeles, CA, United States

  Disclosure information not submitted.

Author(s)

• 

  Nir Horesh, MD

  Resident Physician
  Cleveland Clinic Florida
  Tel Aviv University
  Weston, FL, United States

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

  Andrea Paola P. Solis Pazmino, 1804664892

  Surgery Resident
  Surgery Group Los Angeles
  Porto Alegre, Rio Grande do Sul, Brazil

  Disclosure information not submitted.
• SR

  Sameh Rizkalla, MBBCh, MS, MD, FACS

  Project Scientist
  Cleveland Clinic Florida
  Weston, Florida, United States

  Disclosure information not submitted.
• MB

  Moshe Barnajian, n/a

  Colorectal Surgery
  Surgery Group Los Angeles
  Los Angeles, California, United States

  Disclosure information not submitted.
• JP

  Jamila Piri, B.S.

  Research Assistant
  Surgery Group of LA Research Foundation
  Los Angeles, California, United States

  Disclosure information not submitted.
• 

  Rachel Ma

  Research Coordinator
  Surgery Group of Los Angeles
  Los Angeles, CA, United States

  Disclosure information not submitted.
• KL

  Kristina La, BS

  research fellow
  SGLA
  Los Angeles, California, United States

  Disclosure information not submitted.
• LF

  Luis Armando Figueroa Saraguro, Statistic Subdirector

  Medical Doctor
  CaTaLiNA Research Initiative
  Quito, Pichincha, Ecuador

  Disclosure information not submitted.

ePoster Presenter(s)

• 

  Yosef Nasseri, MD, FACS, FASCRS

  General and colorectal surgeron
  Cedar-Sinai Medical Center
  Cedars-Sinai Medical Center
  Los Angeles, CA, United States

  Disclosure information not submitted.

Purpose/Background: Adjuvant Chemotherapy is gold standard treatment for patients with stage III-IV colorectal cancer (CRC). However, approximately 4-5% of CRC patients exhibit high microsatellite instability (MSI-H) or mismatch repair deficiency (dMMR) that respond well to immune checkpoint blockade. In this study, we aimed to evaluate the benefit of adding PD-1 inhibitor therapy to standard chemotherapy.

Methods/Interventions: We conducted a retrospective analysis of the National Cancer Database (2016-2022), including patients with stage III-IV Colorectal Cancer with MSI-H/dMMR features treated with chemotherapy alone (CH) or chemotherapy plus immunotherapy (CH+I). Propensity score matching (1:1) was used to balance baseline characteristics. The primary outcome was overall survival (OS), evaluated using Kaplan-Meier and Cox proportional hazards models.

Results/Outcomes: A total of 3,447 patients were identified (CH 68.6% vs. CH+I 31.4%) and included for analysis. After matching, 1,080 patients per group were included in each group. Most patients presented with stage IV disease (85%). The CH+I group was younger (median age, 60.0 vs. 62.0 years; p = 0.001), had more grade 3 tumors (37.2% vs. 31.7%; p = 0.002), and a greater comorbidity burden (p = 0.009). In stage III disease, median OS was similar between groups (67.1 vs. 63.6 months, p = 0.53). In stage IV, CH+I was associated with improved median OS (41.8 vs. 34.3 months, p = 0.02) (Fig. 1). On Cox regression analysis, CH+ I was associated with 16% lower risk of death in stage IV (HR = 0.84; 95% CI, 0.72-0.97; p =0.022), but not in stage III patients (HR = 1.59; 95% CI, 0.80-3.16; p=0.186).

Conclusion/Discussion: In this large, national cohort of MSI-H/dMMR CRC, the addition of immunotherapy to chemotherapy was associated with a significant survival benefit in stage IV disease but not in stage III. These findings support chemoimmunotherapy as a rational strategy in metastatic CRC and underscore the need for stage-specific treatment approaches.

Figure 1.