Margin size is an independent predictor of local tumor progression after ablation of colon cancer liver metastases

Abstract

Purpose: This study was designed to evaluate the relationship between the minimal margin size and local tumor progression (LTP) following CT-guided radiofrequency ablation (RFA) of colorectal cancer liver metastases (CLM).

Methods: An institutional review board-approved, HIPPA-compliant review identified 73 patients with 94 previously untreated CLM that underwent RFA between March 2003 and May 2010, resulting in an ablation zone completely covering the tumor 4-8 weeks after RFA dynamic CT. Comparing the pre- with the post-RFA CT, the minimal margin size was categorized to 0, 1-5, 6-10, and 11-15 mm. Follow-up included CT every 2-4 months. Kaplan-Meier methodology and Cox regression analysis were used to evaluate the effect of the minimal margin size, tumor location, size, and proximity to a vessel on LTP.

Results: Forty-five of 94 (47.9 %) CLM progressed locally. Median LTP-free survival (LPFS) was 16 months. Two-year LPFS rates for ablated CLM with minimal margin of 0, 1-5 mm, 6-10 mm, 11-15 mm were 26, 46, 74, and 80 % (p < 0.011). Minimal margin (p = 0.002) and tumor size (p = 0.028) were independent risk factors for LTP. The risk for LTP decreased by 46 % for each 5-mm increase in minimal margin size, whereas each additional 5-mm increase in tumor size increased the risk of LTP by 22 %.

Conclusions: An ablation zone with a minimal margin uniformly larger than 5 mm 4-8 weeks postablation CT is associated with the best local tumor control.

Fig. 1

Minimal margin evaluation method. Minimal margin (M) is the minimum of n margin values (m): m1 = a1–b1, a2–b2, a3–b3, etc. In this demonstrated case, “a3–b3” represents the minimal margin

Fig. 2

Landmark classifications according to reliability

Fig. 3

Total local tumor progression-free survival after ablation

Fig. 4

LTP-free survival curves for different minimal margin

Fig. 5

LTP of CLM after ablation from the site of the minimal margin (82-year-old male). A Preablation CT scan shows a small tumor located in the right hepatic lobe. B Postablation CT shows the expected changes within the ablation zone. C Measuring the distance between the tumor edge and nearest reliable landmark in different directions on pre-CT. D Measuring the distance between the above same landmarks and ablation defect on post-CT; minimal margin was acquired to be 1–5 mm located at approximately 11 o’clock. E, F Five months later, CT and PET all showed local tumor progression at the site of this minimal margin

Fig. 6

Concordant LTP of CLM after ablation at the site of minimal margin (55-year-old male). A Preablation CT scan showed a tumor located in right lobe. B Postablation CT showed the expected changes within the ablation zone; minimal margin was calculated as 6–10 mm located at approximately 9 o’clock. C Eight months later, concordant LTP occurred at the site of minimal margin

Fig. 7

LTP associated with multiple margin after RFA (69-year-old man). A, B Multiple “0” margin (arrow) based on 1-month follow-up CT was demonstrated. C Seven-month follow-up CT showed concordant LTP at the site of the minimal margin

Fig. 8

LTP-free survival curves for single and multiple close margin (<5 mm)