Minimally invasive liver resection for huge (≥10 cm) tumors: an international multicenter matched cohort study with regression discontinuity analyses

Background: The application and feasibility of minimally invasive liver resection (MILR) for huge liver tumours (≥10 cm) has not been well documented. Methods: Retrospective analysis of data on 6,617 patients who had MILR for liver tumours were gathered from 21 international centers between 2009-2019. Huge tumors and large tumors were defined as tumors with a size ≥10.0 cm and 3.0-9.9 cm based on histology, respectively. 1:1 coarsened exact-matching (CEM) and 1:2 Mahalanobis distance-matching (MDM) was performed according to clinically-selected variables. Regression discontinuity analyses were performed as an additional line of sensitivity analysis to estimate local treatment effects at the 10-cm tumor size cutoff. Results: Of 2,890 patients with tumours ≥3 cm, there were 205 huge tumors. After 1:1 CEM, 174 huge tumors were matched to 174 large tumors; and after 1:2 MDM, 190 huge tumours were matched to 380 large tumours. There was significantly and consistently increased intraoperative blood loss, frequency in the application of Pringle maneuver, major morbidity and postoperative stay in the huge tumour group compared to the large tumour group after both 1:1 CEM and 1:2 MDM. These findings were reinforced in RD analyses. Intraoperative blood transfusion rate and open conversion rate were significantly higher in the huge tumor group after only 1:2 MDM but not 1:1 CEM. Conclusions: MILR for huge tumours can be safely performed in expert centers It is an operation with substantial complexity and high technical requirement, with worse perioperative outcomes compared to MILR for large tumors, therefore judicious patient selection is pivotal.