What Constitutes a Clear Margin in Patients With Locally Recurrent Rectal Cancer Undergoing Pelvic Exenteration?

Objectives: To determine what constitutes a clear resection margin (R0) in patients with LRRC. Summary of Background Data: R0 is the most important predictor of survival in patients with LRRC. However, it is not clear what constitutes an R0. A 1-2 mm margin is often used to define R0 but this is based on primary rectal cancer studies. The same definition of R0 is likely inappropriate considering the anatomy and etiology of local recurrences. Methods: A prospective maintained database was reviewed. A R2 margin was defined as macroscopic residual disease. R1 was defined as a microscopically involved margin (0 mm margin) and R0 as at least a 0.1 mm margin. Associations between R status and local recurrence was explored using X-2 test. Associations between margins and overall survival and local recurrence free survival were explored using Kaplan-Meier analysis. Results: There were 210 patients eligible for inclusion for analysis. Of these, 165 (78.6%), 35 (16.7%), and 10 (4.8%) patients had R0, R1, and R2 margins, respectively. Overall survival was significantly different between patients with R0 versus R1 margins but wider resection margins do not confer a survival benefit [57 months (95% confidence interval 38.5-75.5) vs 33 months (95% confidence interval 20.3-45.7), P = 0.03]. Local recurrence free survival was significantly different between patients with R0 versus R1 margins (2- and 5-year local recurrence free survivals of 53.5% and 20.4% vs 25.9% and 14.8%, respectively, P = 0.001 for both). Margins >0.5 mm were not predictive of local recurrence free survival. Conclusions: A microscopically clear resection margin is most important in predicting overall survival. Margins up to 0.5 mm offers a local recurrence benefit but does not confer survival benefit.