A cross-sectional analysis from a real-world cohort of patients with microsatellite instability colorectal cancer (MSI-CRC) with metastatic disease from the Spanish RETUD registry.

178 Background: Survival of microsatellite instability (MSI) metastatic colorectal cancer (mCRC) patients (pts) has remarkably increased with immune checkpoint inhibitors (ICI). Here, we present our real-world data regarding the management and clinical outcomes of a cohort of 214 MSI-mCRC patients included in the Spanish Group of Treatment of Digestive Tumors TTD Registry (RETUD). Methods: RETUD is a national, multicenter registry for gastrointestinal tumors from the Spanish TTD Group. In this cross-sectional analysis we evaluated a real-world cohort of MSI-mCRC pts diagnosed from 1 st January 2017 to 29 th April 2024. Baseline characteristics, treatments and treatment response are descriptively presented. Tumoral response was evaluated according to RECIST 1.1 criteria. First line progression-free survival (PFS) and overall survival (OS) analyzed by Kaplan-Meier method are presented along with 95% confidence intervals (CI). Results: Among 679 MSI-CRC pts included in RETUD, a total of 214 mCRC pts were evaluable. Pts’ age at diagnosis was 69.6 (26-96) years, and they were predominantly Caucasian (97.7%) and female (53.7%). Eastern Cooperative Oncology Group (ECOG) performance status was 0-1 for 168 (78.5%) pts. Seventeen (10.7%) pts presented Lynch syndrome. Main tumor biological characteristics are described at Table 1 and the molecular profile (when available) was: KRAS mutation (24.3%), NRAS mutation (3.5%) and BRAF v600E mutation (53.0%). Surgical resections: 158 (73.8%) pts for primary tumor and 42 (19.6%) pts for metastasis. First line systemic treatment was administered to 187 (97.1%) pts: 92 (49.2%) pembrolizumab, 83 (44.4%) chemotherapy (CT), 4 (2.1%) other ICIs, 8 (4.3%) not reported. With a median follow up period of 17.4 months, the median (95% CI) OS and first-line PFS of the total mCRC population were 32.6 (22-72.4) and 11.1 (8.2-17.9) months (m), respectively. In immunotherapy (IT) pts mOS was not achieved (22.0-NA) and PFS was 26.5 m (12.9-NA) while the mOS was 28.9 m (16.3-69.3) and PFS 7.5 (5.4-9.3) m in CT pts. The overall response rate (ORR) was 54.2% in IT pts vs. 37.3% in CT pts. Conclusions: The introduction of IT has changed the evolution of MSI-H mCRC management, offering a beneficial impact in the OS and PFS survival in contrast to other conventional therapies in a real-world context. Tumor characteristics at initial diagnosis of CRC. Stage at initial diagnosis of CRC I/II, n (%) 4 (1.9) / 26 (12.1) III/IV, n (%) 66 (30.8) / 118 (55.1) Location of primary tumor a , n (%) right colon /left colon /rectum 160 (74.8) /37 (17.3) /19 (8.9) Main metastatic location b , n (%) Liver 84 (39.3) Peritoneal 76 (35.5) Lymph 71 (33.2) Lungs 41 (19.2) a Pts with more than 1 primary tumor; the percentage may be over 100%. Data missing for 4 (1.9%) pts. b Pts with more than 1 metastatic site; the percentage may be over 100%.