On-site recurrence risk after parenchymal R1 liver resection for colorectal metastases.

Background: Histologic microscopic positive resection margin is a debated prognostic factor in patients resected for colorectal liver metastases. This study aimed to assess whether patients with R1 resection experience recurrence at the site of the resection (on-site recurrence) and to identify predictive factors for recurrence profiles in patients with R1 margins after resection of colorectal liver metastases.

Methods: All surgical colorectal liver metastasis resection cases with R1 parenchymal margin from September 2014 to March 2020 in our center were retrospectively included. Imaging was reviewed for each metastasis. All the analyses were performed per metastasis. Recurrence location was examined for each metastasis according to the site of the R1 margin and defined as on-site when recurrence was at the same place of the resected lesion. Prognostic factors for recurrence type were assessed using logistic regression.

Results: Of 700 patients who underwent liver resection for colorectal liver metastases, 105 (15%) had at least 1 metastasis with R1 resection margin, representing 6.8% per metastasis. The median follow-up was 34 months. Overall recurrence occurred in 130 metastases (83.3%) with intrahepatic recurrence in 106 metastases (80.9%). On-site recurrence was observed for 49 metastases (31.4%) and isolated (without an additional recurrence site) for 20 metastases (12.8%). The on-site recurrence did not impact overall survival. Three predictive factors for on-site recurrence were found in the multivariate logistic regression: synchronous metastases, nonanatomic resection, and pathologic response tumor regression grade 4-5.

Conclusion: Intrahepatic localization of recurrence is more frequent than on-site recurrence after R1 parenchymal resection. Synchronous metastases, nonanatomic resection, and tumor regression grade 4-5 may impact the risk of on-site recurrence.