Local recurrence rates following laparoscopic ultrasound-guided microwave ablation for hepatic metastases of colorectal adenocarcinoma

Abstract

Background: For patients with oligometastatic colorectal adenocarcinoma (CRC) isolated to the liver, local therapy including hepatic resection and local ablative procedures are recommended, though patients with tumors larger than 3cm have been shown to have higher local recurrence rates with ablation. Historically, radiofrequency ablation (RFA) was the predominant ablative modality chosen, but more recently, microwave ablation (MWA) has begun to supplant RFA due to a number of advantages. This study primarily aims to evaluate the local recurrence rate of this modality in our institution. Methods: A retrospective review was conducted of patients who underwent laparoscopic MWA from 2007 to 2018 at Carolinas Medical Center, a major regional quaternary care facility with hepatopancreatobiliary surgical subspecialty care within the Atrium Health System. Patients were identified from medical records containing the International Classification of Disease (ICD)-9 and 10 codes for colorectal adenocarcinoma and the current procedural terminology (CPT) code for laparoscopic ablation of liver tumors (47370), which was exclusively performed using MWA under ultrasound guidance at our facility during this time period. Retrospective chart review was used to identify demographic, perioperative, and postoperative clinical outcomes data. Patients were divided into two groups: patients with all tumors ≤3 cm and patients with at least one tumor >3 cm. Data were then analyzed using STATA. Results: A total of 167 patients with 328 tumors underwent MWA from 2007–2018 with an average follow up of 17.7 months (range: 0-80mos). 142 patients with a combined 279 tumors were included in the ≤3 cm group, while 25 patients with a combined 49 tumors were included in the >3cm group. Patients in the ≤3 cm group were significantly younger than those with larger tumors (median age 58 vs. 69, p = 0.002). There were no other significant demographic differences between the two groups. The majority of patients had only 1 tumor ablated (range: 1 to 14). There was no difference between the two groups in median number of tumors ablated. Median operative time was 115 minutes in the ≤3 cm group and 104 minutes in the >3 cm group (p = 0.702). Incomplete ablation, defined as residual tumor at the time of initial reimaging following MWA, was lower for the ≤3cm group, but this did not reach statistical significance (2.9% vs. 8.0%, p = 0.220). Most notably, there was a significant discrepancy between the two groups in local recurrence rates. Expressed as number of recurrences over number of tumors ablated for each group, significantly fewer tumors in the ≤3 cm group recurred locally (11.8% vs. 30.3%, p = 0.008). This represents local recurrence in 24 (17.9%) patients in the ≤3 cm group, and in 10 (40.0%) patients in the >3 cm group, p = 0.013. Conclusion: Numerous studies have demonstrated the safety and efficacy of local thermal ablative techniques, predominantly RFA, for oligometastatic CRC to the liver. Several recent studies have demonstrated promising results for MWA as well. Data from our retrospective series suggests that local recurrence rates in patients with tumors ≤3 cm who underwent MWA are comparable to those reported in the literature for patients undergoing hepatic resection, while those with larger tumors have notably higher local recurrence rates. While at least one multicenter randomized controlled trial to compare surgical resection with thermal ablation is ongoing, our institutional experience indicates that MWA is an effective treatment modality in patients with CRC metastases ≤3 cm.