Impact of 3 mm margin on risk of recurrence and survival in oral cancer

Introduction: While positive surgical margins in oral squamous cell carcinoma (OSCC) is generally considered an adverse prognosticator, the significance of close (≤5 mm) margins is more debatable, and has not been widely adopted as an indicator for radiotherapy. Materials and methods: Retrospective study of 244 patients undergoing primary surgical resection of OSCC. The impact on local control (LC), disease-specific survival (DSS) and overall survival (OS) of margins at 1 mm intervals was studied. Results: 65 patients had involved (<1 mm), 119 close (1–5 mm), and 60 clear (>5 mm) main specimen margins. Involved margins was predictive of DSS (p = 0.04), but not LC (p = 0.20) or OS (p = 0.09). Both the 2 mm and 3 mm margin cut-offs were significantly associated with LC (p = 0.02, and p = 0.01), DSS (p = 0.02, and p = 0.007), and OS (p = 0.03. and p = 0.005). In a 3-tier model, use of 3 mm for demarcation between close and clear yielded good separation between survival curves of clear (≥3 mm), and close (1-<3 mm) or involved (<1 mm). Final margins, determined after incorporation of frozen sections and extra margins taken separately, was significant for LC (p = 0.04), but not for DSS (p = 0.05) or OS (p = 0.17). On multivariate analysis, <3 mm margin, T-classification, nodal status, extranodal spread, and postoperative radiotherapy, were independent predictors of DSS and OS. For LC, only T-classification was significant. Conclusion: A 3 mm main specimen margin is significantly associated with survival in OSCC and may be useful for demarcation between close and clear. Further study is required to determine any impact on survival of radiotherapy for patients with <3 mm margins as sole indicator for radiotherapy.