Table 1.

Summary of included studies

Ref.	Study design	Country	Subject characteristics	Definitions used for frailty	Sample size	Newcastle Ottawa quality score
Okada et al[17], 2024	Prospective cohort	Japan	Median age of 73 years; males (74%); indication for surgery - HCC; the majority with laparoscopic surgery (60.0%; proportion with laparoscopic surgery higher in non-frail subjects); extent of resection similar in two groups; no differences in age, sex, underlying hepatic diseases, or proportion of patients with comorbidities in two groups	Assessed using KCL tool (phenotypic frailty index; self-administered questionnaire comprising 25 items); score of ≥ 8 points - frail; score of < 7 points - non-frail	Frailty: 25; no frailty: 56	7
Shahrestani et al[18], 2023	Retrospective cohort	United States	Mean age of 62 years; males (51%); indication for surgery - liver metastasis; type of surgery not specified	JHACG frailty-defining diagnosis indicator was used. It uses 10 categories of ICD-10 codes to predict a patient’s frailty status	Frailty: 766; no frailty: 749	7
Osei-Bordom et al[19], 2022	Retrospective cohort	United Kingdom	Median age of 65.3 years; males (57%); most common indication for surgery - colorectal liver metastases followed by HCC; the majority undergoing open surgery (86.0%; proportion similar in two groups); extent of resection similar in two groups (P = 0.20); those classified as frail had increased BMI and prevalence of hypertension, diabetes, and COPD	MFI used: Patients stratified based on an mFI cut-off - frail (mFI ≥ 1) and robust (mFI = 0)	Frailty: 634; no frailty: 1192	8
Hosoda et al[20], 2022	Prospective cohort	Japan	Median age of 71 years; males (65%); indication for surgery - perihilar cholangiocarcinoma; type of surgery not specified; extent of resection similar in two groups; those with frailty had higher ASA classification; no differences in proportion of patients with comorbidities (hypertension and DM) in two groups	Assessed using CFS. Score of 3 to 9 points - frail; score of 1 to 2 points - non-frail	Frailty: 44; no frailty: 35	7
Madrigal et al[21], 2022	Retrospective cohort	United States	Mean age of 72 years; males (52%); most frail patients were male and had malignant liver disease as the indication for resection; compared with their non-frail counterparts, frail patients were older and had higher burden of comorbidities	JHACG frailty-defining diagnosis indicator	Frailty: 3655; no frailty: 37080	7
Maegawa et al[22], 2022	Retrospective cohort	United States	Patients underwent hepatectomy due to primary hepatobiliary cancer or secondary liver metastasis; open surgery in the majority (> 80%); mean age of 59 years; males (51%)	mFI-5: MFI = 0 indicated no frailty; mFI ≥ 1 indicated frailty	Frailty: 11687; no frailty: 12463	8
Dauch et al[23], 2022	Retrospective cohort	United States	Patients underwent minor hepatectomy; open surgery (82%); mean age of 58 years; males (58%); patients with frailty had higher ASA classification	mFI-5: MFI = 0 indicated no frailty; mFI ≥ 2 indicated frailty	Frailty: 654; no frailty: 2737	8
Yamada et al[24], 2021	Retrospective cohort	Japan	Mean age of 80 years; males (62%); similar burden of comorbidities (diabetes and hypertension) in two groups; primary indication for surgery - HCC; similar tumour characteristics in two groups; mean follow-up of 2.6 years	Assessed using CFS; score of ≥ 4 points - frail	Frailty: 21; no frailty: 71	7
McKechnie et al[25], 2021	Retrospective cohort	Canada	Patients with liver resection mainly due to HCC and colorectal cancer liver metastasis; median age of 64 years; females (45%); mean BMI of 28 kg/m2; laparoscopic resection (57%); median number of liver segments resected similar in two groups; patients with low mFI were younger, had lower ASA class, and were more likely to have > 4 METS on exercise tolerance testing, and less likely to be smokers	MFI used: Patients stratified based on an mFI cut-off - frail (mFI ≥ 0.27) and robust (mFI < 0.27)	Frailty: 58; no frailty: 351	7
Tokuda et al[26], 2021	Retrospective cohort	Japan	Mean age of 70 years; males (63%); burden of comorbidities (diabetes and hypertension) higher in frail group; primary indication for surgery - colorectal liver metastasis; mean follow-up of 46 mo	Assessed using CFS. Score of ≥ 4 points - frail	Frailty: 29; no frailty: 58	7
Okabe et al[27], 2019	Retrospective cohort	Japan	Mean age of 75 years; males (74%); indication for surgery - liver metastasis from colorectal cancer; mean BMI of subjects 23 kg/m2; type of surgery not specified; extent of resection similar in two groups	Assessed using CFS; score of ≥ 4 points - frail	Frailty: 16; no frailty: 127	6
Chen et al[28], 2018	Retrospective cohort	United States	Patients underwent liver and colorectal resection (for colorectal cancer with liver metastasis); open surgery (86%); mean age of 59 years; males (55%); patients with frailty were older, and had higher ASA classification, higher BMI, and greater number of comorbidities (hypertension, COPD, and DM)	5-item mFI; mFI = 0 indicated no frailty; mFI ≥ 2 indicated frailty	Frailty: 225; no frailty: 1063	8
Louwers et al[29], 2016	Retrospective cohort	United States	Mean age of 58 years; males (49%); indication for surgery - primary hepatic malignancy and liver metastasis; open hepatectomy in the majority	MFI used: Patients stratified based on an mFI cut-off- frail (mFI ≥ 1) and robust (mFI = 0)	Frailty: 6150; no frailty: 4150	6

mFI: Modified frailty index; COPD: Chronic obstructive pulmonary disease; DM: Diabetes mellitus; ASA: American Society of Anaesthesia; BMI: Body mass index; CFS: Clinical Frailty Scale; METS: Metabolic equivalents; HCC: Hepatocellular cancer; mFI-5: 5-point Modified Frailty Index; JHACG: Johns Hopkins Adjusted Clinical Groups; ICD-10: International Classification of diseases-10; KCL: Kihon Checklist.