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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 between local recurrence (LR) rates and different distances of invasive tumor from surgical margin is not well characterized.To analyze the association between specific distances from invasive tumor to surgical margin and LR in patients with OCSCC.Retrospective cohort study of 432 patients treated via en bloc resection for OCSCC between 2005 and 2014 at the University of Iowa Hospitals and Clinics. In all cases, permanent margin evaluation was performed on the main tumor specimen and with intraoperative frozen section margin assessment from the tumor bed.The LR rate based on minimum millimeter distance between invasive tumor and inked main specimen margin.Of the 432 participants, 252 (58%) were men and 180 (42%) were women (mean age, 62.14 years; range, 19-99 years). In each case, 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 microscopic positive margins was 44% (95% CI, 34%-55%); for margins less than 1 mm, 28% (95% CI, 18%-41%); for 1 mm, 17% (95% CI, 8%-31%); for 2 mm, 13% (95% CI, 6%-27%); for 3 mm, 13% (95% CI, 5%-32%); for 4 mm, 14% (95% CI, 5%-35%); and for 5 mm or greater, 11% (95% CI, 6%-18%). Analysis of the receiver operating characteristic curve identified a cutoff of less than 1 mm as appropriate for classifying higher risk of local recurrence. Regardless of margin distance, resection of additional tissue beyond 1 mm based on intraoperative frozen section was not associated with improved local control.The commonly used cutoff of 5 mm for a close margin lacks an evidential basis 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 significant difference for greater distances. This study suggests that a cutoff of less than 1 mm identifies patients at increased local recurrence risk who may benefit from additional treatment. Analysis of the tumor specimen rather than the tumor bed is necessary for this determination.