The Importance of Optimal Thermal Ablation Margins in Colorectal Liver Metastases: A Systematic Review and Meta-Analysis of 21 Studies

Abstract

Background: Colorectal cancer (CRC) is the second most common cause of cancer-related deaths in the US. Thermal ablation (TA) can be a comparable alternative to partial hepatectomy for selected cases when eradication of all visible tumor with an ablative margin of greater than 5 mm is achieved. This systematic review and meta-analysis aimed to encapsulate the current clinical evidence concerning the optimal TA margin for local cure in patients with colorectal liver metastases (CLM).

Methods: MEDLINE, EMBASE, and the CENTRAL databases were systematically searched from inception until 1 May 2023, in accordance with the PRISMA Guidelines. Measure of effect included the risk ratio (RR) with 95% confidence interval (CI) using the random-effects model.

Results: Overall, 21 studies were included, comprising 2005 participants and 2873 ablated CLMs. TA with margins less than 5 mm were associated with a 3.6 times higher risk for LTP (n = 21 studies, RR: 3.60; 95% CI: 2.58-5.03; p-value < 0.001). When margins less than 5 mm were additionally confirmed by using 3D software, a 5.1 times higher risk for LTP (n = 4 studies, RR: 5.10; 95% CI: 1.45-17.90; p-value < 0.001) was recorded. Moreover, a thermal ablation margin of less than 10 mm but over 5 mm remained significantly associated with 3.64 times higher risk for LTP vs. minimal margin larger than 10 mm (n = 7 studies, RR: 3.64; 95% CI: 1.31-10.10; p-value < 0.001).

Conclusions: This meta-analysis solidifies that a minimal ablation margin over 5 mm is the minimum critical endpoint required, whereas a minimal margin of at least 10 mm yields optimal local tumor control after TA of CLMs.

Keywords: colorectal cancer; interventional oncology; liver metastases; margin; systematic review; thermal ablation.

Figure 1

PRISMA Flowchart depicting the detailed study selection process.

Figure 2

Forest plot of the pooled estimate of the local tumor progression rates between <5 mm vs. ≥5 mm thermal ablation margins (“*”: second study with the same first author and release date).

Figure 3

(A) Forest plot of the pooled estimate of the local tumor progression rates between <5 mm vs. ≥5 mm thermal ablation margins assessed using 3D software techniques. (B) Forest plot of the pooled estimate of the local tumor progression rates between <5 mm vs. ≥5 mm thermal ablation margins assessed using 2D software techniques. (“*”: second study with the same first author and release date).

Figure 4

Forest plot of the pooled estimate of the local tumor progression rates between <5 mm vs. ≥5 mm thermal ablation margins assessed in patients with confirmed KRAS mutation.

Figure 5

(A) Forest plot of the pooled estimate of the local tumor progression rates between <10 mm vs. ≥10 mm thermal ablation margins assessed. (B) Forest plot of the pooled estimate of the local tumor progression rates between ≥5 mm and <10 mm vs. ≥10 mm thermal ablation margins assessed.