Percutaneous Radiofrequency Ablation of Colorectal Cancer Liver Metastases: Factors Affecting Outcomes--A 10-year Experience at a Single Center

Abstract

Purpose: To identify predictors of oncologic outcomes after percutaneous radiofrequency ablation (RFA) of colorectal cancer liver metastases (CLMs) and to describe and evaluate a modified clinical risk score (CRS) adapted for ablation as a patient stratification and prognostic tool.

Materials and methods: This study consisted of a HIPAA-compliant institutional review board-approved retrospective review of data in 162 patients with 233 CLMs treated with percutaneous RFA between December 2002 and December 2012. Contrast material-enhanced CT was used to assess technique effectiveness 4-8 weeks after RFA. Patients were followed up with contrast-enhanced CT every 2-4 months. Overall survival (OS) and local tumor progression-free survival (LTPFS) were calculated from the time of RFA by using the Kaplan-Meier method. Log-rank tests and Cox regression models were used for univariate and multivariate analysis to identify predictors of outcomes.

Results: Technique effectiveness was 94% (218 of 233). Median LTPFS was 26 months. At univariate analysis, predictors of shorter LTPFS were tumor size greater than 3 cm (P < .001), ablation margin size of 5 mm or less (P < .001), high modified CRS (P = .009), male sex (P = .03), and no history of prior hepatectomy (P = .04) or hepatic arterial infusion chemotherapy (P = .01). At multivariate analysis, only tumor size greater than 3 cm (P = .01) and margin size of 5 mm or less (P < .001) were independent predictors of shorter LTPFS. Median and 5-year OS were 36 months and 31%. At univariate analysis, predictors of shorter OS were tumor size larger than 3 cm (P = .005), carcinoembryonic antigen level greater than 30 ng/mL (P = .003), high modified CRS (P = .02), and extrahepatic disease (EHD) (P < .001). At multivariate analysis, tumor size greater than 3 cm (P = .006) and more than one site of EHD (P < .001) were independent predictors of shorter OS.

Conclusion: Tumor size of less than 3 cm and ablation margins greater than 5 mm are essential for satisfactory local tumor control. Tumor size of more than 3 cm and the presence of more than one site of EHD are associated with shorter OS.

Figure 1a:

Example of ablative margin measurement in a 74-year-old man with a 2.7-cm tumor. (a) Axial portal venous phase CT image shows the tumor before RFA; distances 1, 2, and 3 were measured from the edges of the tumor to the chosen landmarks. (b) Axial portal venous phase CT image obtained 5 weeks after RFA shows the ablation defect; the same distances 1, 2, and 3 were measured from the edge of the ablation defect to the same landmarks. The corresponding distances were subtracted, and the smallest value was chosen as the minimal margin—that is, distance 1 (16.3 mm – 12.5 mm = 3.8 mm). (c) Axial portal venous phase CT image obtained 4.5 months after RFA shows LTP (arrow) at the same site of the insufficient margin (distance 1).

Figure 1b:

Example of ablative margin measurement in a 74-year-old man with a 2.7-cm tumor. (a) Axial portal venous phase CT image shows the tumor before RFA; distances 1, 2, and 3 were measured from the edges of the tumor to the chosen landmarks. (b) Axial portal venous phase CT image obtained 5 weeks after RFA shows the ablation defect; the same distances 1, 2, and 3 were measured from the edge of the ablation defect to the same landmarks. The corresponding distances were subtracted, and the smallest value was chosen as the minimal margin—that is, distance 1 (16.3 mm – 12.5 mm = 3.8 mm). (c) Axial portal venous phase CT image obtained 4.5 months after RFA shows LTP (arrow) at the same site of the insufficient margin (distance 1).

Figure 1c:

Example of ablative margin measurement in a 74-year-old man with a 2.7-cm tumor. (a) Axial portal venous phase CT image shows the tumor before RFA; distances 1, 2, and 3 were measured from the edges of the tumor to the chosen landmarks. (b) Axial portal venous phase CT image obtained 5 weeks after RFA shows the ablation defect; the same distances 1, 2, and 3 were measured from the edge of the ablation defect to the same landmarks. The corresponding distances were subtracted, and the smallest value was chosen as the minimal margin—that is, distance 1 (16.3 mm – 12.5 mm = 3.8 mm). (c) Axial portal venous phase CT image obtained 4.5 months after RFA shows LTP (arrow) at the same site of the insufficient margin (distance 1).

Figure 2a:

Graphs show Kaplan-Meier curves for LTPFS classified by (a) tumor size, (b) ablation margin size, (c) modified CRS, and (d) time period (before or after November 2009).

Figure 2b:

Graphs show Kaplan-Meier curves for LTPFS classified by (a) tumor size, (b) ablation margin size, (c) modified CRS, and (d) time period (before or after November 2009).

Figure 2c:

Graphs show Kaplan-Meier curves for LTPFS classified by (a) tumor size, (b) ablation margin size, (c) modified CRS, and (d) time period (before or after November 2009).

Figure 2d:

Graphs show Kaplan-Meier curves for LTPFS classified by (a) tumor size, (b) ablation margin size, (c) modified CRS, and (d) time period (before or after November 2009).

Figure 3a:

Graphs show Kaplan-Meier survival curves for OS classified by (a) liver progression status and re-treatment with percutaneous RFA, (b) tumor size, (c) modified CRS (score of 0 or 1 = low risk, score of 2 or 3 = intermediate risk, and score of 4 or 5 = high risk), and (d) EHD site(s).

Figure 3b:

Graphs show Kaplan-Meier survival curves for OS classified by (a) liver progression status and re-treatment with percutaneous RFA, (b) tumor size, (c) modified CRS (score of 0 or 1 = low risk, score of 2 or 3 = intermediate risk, and score of 4 or 5 = high risk), and (d) EHD site(s).

Figure 3c:

Graphs show Kaplan-Meier survival curves for OS classified by (a) liver progression status and re-treatment with percutaneous RFA, (b) tumor size, (c) modified CRS (score of 0 or 1 = low risk, score of 2 or 3 = intermediate risk, and score of 4 or 5 = high risk), and (d) EHD site(s).

Figure 3d:

Graphs show Kaplan-Meier survival curves for OS classified by (a) liver progression status and re-treatment with percutaneous RFA, (b) tumor size, (c) modified CRS (score of 0 or 1 = low risk, score of 2 or 3 = intermediate risk, and score of 4 or 5 = high risk), and (d) EHD site(s).