Improved survival with immunotherapy for microsatellite unstable colorectal cancer with peritoneal metastases

Abstract

Background: KEYNOTE-177 demonstrated that immunotherapy was superior to chemotherapy for microsatellite-instability-high (MSI-high) metastatic colorectal cancer. Colorectal cancer with peritoneal metastases (CRPM) has a poorer prognosis than other metastatic sites, with an unclear role of immunotherapy. We evaluated trends in immunotherapy use and overall survival (OS). Methods: Patients with CRPM and MSI testing were identified in the National Cancer Database (2016−2020). We evaluated immunotherapy use by year and associated patient/hospital factors. OS was compared for immunotherapy versus chemotherapy, cytoreductive surgery (CRS), and immunotherapy plus CRS. Results: Among 15 322 CRPM patients, 7072 (46.2%) patients had documented MSI testing, with 819 (11.6%) MSI-high. Ninety-eight MSI-high patients received immunotherapy alone (12.3%), increasing from 0% in 2016 to 19.1% in 2020 (p < 0.01). On multivariable analysis, only higher comorbidity was associated with immunotherapy (OR: 2.83 [1.22−6.52]). Two-year OS with immunotherapy versus chemotherapy was 64.2% versus 54.1% (p < 0.05). In patients receiving CRS plus systemic therapy (N = 96), 2-year OS was 68.4%. Among patients who underwent immunotherapy and CRS versus immunotherapy alone, 2-year OS was 80.0% versus 60.0% (p = 0.14). Conclusions: Immunotherapy was associated with significantly better survival compared to chemotherapy in MSI-high CRPM. Two-year OS with systemic + CRS was 68.4%. Despite its role in guiding treatment, MSI testing remains low for these patients.