Ablative techniques in Colorectal Liver Metastases: A Systematic Review and Descriptive Summary of Practice

Background In the UK, over 40,000 patients are diagnosed with colorectal cancer annually. Many of these patients develop liver metastases. Although surgical resection is the gold-standard treatment for colorectal liver metastasis (CRLM), some patients are unsuitable for resection. Radiofrequency Ablation (RFA) and Microwave Ablation (MWA) are alternative treatments for CRLM. However, consensus is lacking regarding selection criteria, tumour characteristics, ablation technique delivery, and device settings. This systematic review summarises current evidence regarding selection criteria, treatment indications, and ablation delivery to inform future prospective studies. Methods A systematic review was conducted following PRISMA guidelines. Studies assessing RFA and MWA treatment of CRLM were identified in Medline, Embase, Web of Science and the Cochrane database of systematic reviews, from inception until 1st June 2021. Eligible studies included those reporting patient selection, tumour characteristics, treatment delivery, ablation device settings, and ablation outcomes for CRLM. Data extraction and analysis were performed. Results Forty-six studies were included (retrospective cohort n=40, prospective cohort n=4, non-randomized comparative studies n=2). Fifty-four inclusion criteria were used across 39 studies and were not stated in 7 studies. Tumours varied in mean number (1-8) and diameter (1.54-4.35cm). Neoadjuvant chemotherapy use (10-100% of patients), ablation delivery approach (Open n=4, laparoscopic n=11, percutaneous n=23, mixed n=2), anaesthetic mode (GA n=17, LA n=9, mixed n=2) and delivering clinician (radiologist n=8, surgeon n=15) all varied. Thirty studies lacked complete ablation device settings. Six studies followed a standardised ablation algorithm and 10 studies had specific settings. Five-year survival ranged from 0-69.7% for ablation. Conclusions There is significant heterogeneity in study design, patient selection, and ablation techniques for CRLM. The lack of standardized approaches and inconsistent reporting of methodology and outcomes make it challenging to determine the optimal ablative treatment for CRLM. Future research should focus on clearly defining selection and treatment criteria, as well as treatment delivery to facilitate generalisability. An RCT investigating ablation techniques may be difficult to implement due to a lack of clinician and patient equipoise, however, a high-quality, multi-centre nationwide prospective cohort study to investigate ablation as an alternative to surgery is required for high-risk patients with CRLM.