Importance: There is a lack of consistency in the literature regarding the definition of ‘close’ resection margins in the surgical treatment of oral cavity squamous cell carcinoma (OCSCC), and the relationship of the distance between invasive tumor and surgical margin with local recurrence (LR) rate is not well characterized.
Objective: To analyze the relationship between the specific distance from invasive tumor to surgical margin and LR in a cohort of patients with OCSCC.
Design, Setting, and Participants: Retrospective cohort study of 406 patients treated via en bloc resection for OCSCC between 2005-2014 at the University of Iowa Hospitals and Clinics, and in whom permanent margin evaluation was performed on the main tumor specimen and intraoperative frozen section margin assessment from the tumor bed.
Main Outcomes and Measures; LR rate based on minimum millimeter distance between invasive tumor and the inked main specimen margin.
Results: The LR rate was analyzed in relation to each millimeter distance of invasive cancer from the inked main specimen margin, with results showing an exponential inverse relationship. The LR rate for positive margins was 0.46 (95% CI 0.34-0.57); for <1 mm, 0.27 (95% CI 0.16-0.41); for 1 mm, 0.15 (95% CI 0.06-0.31); for 2 mm, 0.18 (95% CI 0.08-0.35); for 3 mm, 0.10 (95% CI 0.02-0.32); for 4 mm, 0.15 (95% CI 0.04-0.39); and for >5 mm, 0.12 (95% CI 0.06-0.21). Compared to patients with margins ≥5 mm, patients with tumor extending to the inked edge on the main specimen had a relative risk (RR) of local recurrence of 3.9 (95% CI 2.1-7.3); for distances of <1 mm, the RR was 2.29 (1.1-4.7); for 1 mm, 1.27 (0.5-3.3); for 2 mm, 1.57 (0.6-3.8); for 3 mm, 0.81 (0.2-3.4); and for 4 mm, 1.27 (0.4-4.2). Analysis of the receiver operating curve identified that a cutoff of <1 mm is most appropriate for classifying a higher risk of local recurrence. The predictive power of resection margin distance for local recurrence based on an area under the curve calculation is 0.69.
Conclusions and Relevance: The commonly used cutoff of 5 mm for a close margin appears to lack an evidential basis or utility in predicting local recurrence. Invasive tumor within 1 mm of the permanent specimen margin is associated with a significantly higher local recurrence rate, though there is no statistically significant difference for distances greater than that. This study suggests a cutoff of <1 mm close distance identifies patients at increased risk of local recurrence, who should be considered for adjuvant treatment. Analysis of the tumor specimen rather than the tumor bed is necessary for this determination.