Study—International Multicentric Minimally Invasive Liver Resection (SIMMILR-4): A Comparison of Open, Minimally Invasive, Cobotic and Robotic-Assisted Surgery for Colorectal Liver Metastases

Introduction: This international multicenter study compared five surgical approaches for liver resection in colorectal metastases: open (O), standard laparoscopy (L), laparoscopy with 3D imaging (3D), laparoscopy with single robotic-arm assistance (1RA), and with complete robotic systems utilizing 4 robotic arms(4RA). A subcohort analysis was done for enhanced L, this cohort was termed collaborative assisted robotics (cobotic surgery) and consisted of L with the addition of 3D imaging or a single robotic arm to hold the laparoscope. This study aimed to evaluate whether 4RA offers any significant advantages over laparoscopy with and without cobotic enhancements. Methods: We analyzed 1,257 patients across five centers using propensity score matching. Surgical approaches were compared for blood loss, operative time, hospital stay, resection margins (R0 status), and major complications (Clavien-Dindo grade ≥3). Statistical analysis used Student's t-test and Mann-Whitney U-test for continuous variables, with p<0.05 considered significant. Results: Minimally invasive techniques without 3-D imaging, a solitary robotic arm to hold the laparoscope or utilization of handheld robotic GIA staplers showed superior outcomes to open surgery. Laparoscopic approaches demonstrated significantly reduced blood loss (L: 553 mL vs O: 695 mL, p<0.001) and shorter hospital stays when compared to open surgery (L: 8 days vs O: 14 days, p<0.001). The 4RA cohort had similar benefits when compared to O resection (blood loss: 382 mL vs 542 mL, p<0.001; LOS: 8 vs 24 days, p<0.001), but longer operative times (280 vs 305 minutes (min), p<0.001). The 1RA and 3D approaches showed comparable outcomes to 4RA in most measures. Conclusions: While robotic assistance offers technical advantages, complete robotic systems (4RA) did not demonstrate clear superiority over laparoscopy with or without cobotics. Cost-effective modular enhancements to standard laparoscopy may provide future benefits while allowing resource allocation toward AI-driven surgical innovations. Future studies should employ prospective designs with standardized protocols to validate these findings and assess long-term oncologic outcomes.