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Page 4 of 11 Sawa et al. Mini-invasive Surg 2024;8:30 https://dx.doi.org/10.20517/2574-1225.2024.43

Table 1. Demographics and clinicopathologic characteristics between OLR and MISLR groups
OLR N = 781 MISLR N = 172 P-value
Age, median (IQR), year 69 (61-75) 68 (59-76) 0.625
Sex, n (%) 0.449
Male 554 (70.9) 117 (68.0)
Female 227 (29.1) 55 (32.0)
BMI, median (IQR), kg/m 2 22.9 (20.6-25.3) 23.0 (21.0-25.9) 0.333
Child-pugh-score, n (%) > 0.999
A 770 (98.6) 170 (98.8)
B 11 (1.4) 2 (1.2)
ICG-R15, median (IQR), % * 9.7 (6.6-14.2) 9.9 (5.7-14.0) 0.391
History of abdominal surgery, n (%) 364 (46.6) 89 (51.7) 0.222
ASA, n (%) 0.075
1 114 (14.6) 23 (13.4)
2 567 (72.6) 115 (66.9)
3 99 (12.7) 33 (19.2)
4 1 (0.1) 1 (0.6)
Diagnosis, n (%) 0.061
HCC 470 (60.2) 89 (51.7)
ICC 70 (9.0) 12 (7.0)
CLM 164 (21.0) 45 (26.2)
NENM 3 (0.4) 2 (1.2)
†
Others 74 (9.5) 24 (14.0)
* †
Data missing on ICG-R15 for four patients in OLR group. Including non-colorectal liver metastases, focal nodular hyperplasia, hepatic
hemangioma, bile duct stones, angiolipoma, angiomyolipoma, mucinous cystic neoplasm, neurofibroma, and inflammation tissue. OLR: Open liver
resection; MISLR: minimally invasive liver resection; IQR: interquartile range; BMI: body mass index (calculated as weight in kilograms divided by
height in meters squared); ICG-R15: indocyanine green retention rate at 15 minutes; ASA: American Society of Anesthesiologists; HCC:
hepatocellular carcinoma; ICC: intrahepatic cholangiocarcinoma; CLM: colorectal liver metastases; NENM: neuroendocrine neoplasm metastases.

Statistical analysis
Categorical variables were expressed in numbers and percentages, and assessed with Pearson’s Chi-squared
test or Fisher’s exact test. Continuous variables were expressed as median values with the interquartile range
(IQR), and assessed with Kruskal-Wallis test. Cochran-Armitage test was used for a trend test of binary
variables, and Jonckheere-Terpstra test was used for a trend test of continuous variables. Statistical analysis
was conducted with R software (The R Foundation).

RESULTS
Study population
Of the 1,866 patients who underwent liver resection, 953 met the inclusion criteria
[Supplementary Figure 1]. Of the 953 included patients, 781 underwent OLR (grade I, n = 224; grade II, n =
172; grade III, n = 385) and 172 underwent MISLR (grade I, n = 105; grade II, n = 47; grade III, n = 20). The
demographic and clinicopathologic characteristics did not significantly differ between the groups [Table 1].
Both groups included 50%-70% of patients with primary liver cancer and 20%-30% of patients with
metastatic liver cancer.

Annual number of MISLRs performed according to complexity grades
The indications for MISLR had expanded from low-complexity resections to intermediate- and high-
complexity resections. The proportion of grade II (intermediate-complexity) resections has increased since