Objectives: To determine the incidence of positive surgical margins in submandibular gland malignancies, identify patient, tumor, and facility factors associated with positive margins, and associate positive margins with overall survival.
Study Design: Retrospective analysis of the National Cancer Database (NCDB).
Methods: Adult patients treated with surgery for a submandibular gland malignancy were identified in the NCDB 2004-2014. Multivariable logistic regression was used to evaluate predictors of positive margins. Positive margin rates were determined and compared between academic and non-academic facilities. Cox proportional hazards regression was used to calculate overall survival by margin status.
Results: We identified 1,150 patients with submandibular malignancy undergoing surgical resection. Overall positive margin rate was 41%. By facility, positive margin rate ranged from 0% to 100% with a median of 33% [interquartile range (IQR): 25%– 67%]. The median(IQR) positive margin rates for academic and nonacademic facilities were 33% (25%– 50%) and 33% (IQR: 29%-67%), respectively. On multivariable analysis, increased odds of positive margins were seen in patients with more advanced T stage (versus T1, T3: odds ratio [OR]: 3.04, [95% confidence interval (CI): 2.18-4.25], p<0.001; T4a: OR: 2.89, [95% CI: 1.71-4.89], p<0.001), and adenoid cystic carcinoma histology (OR: 1.54, [95% CI: 1.07-2.21], p=0.02). Patients who underwent a diagnostic biopsy prior to surgery had a decreased odds of positive margins (OR: 0.72; [95% CI: 0.55-0.94], p=0.014). Treatment at a nonacademic facility was also associated with increased likelihood of positive margins (OR:1.41 [95% CI: 1.10-1.82], p=0.007). Adjuvant therapy (radiation therapy with or without chemotherapy) was administered to 77% and 63% of patients with positive and negative margins, respectively. Positive margins were associated with reduced overall survival (OS), (58% vs. 69% 5-year OS, hazard ratio [HR]: 1.37 [95% CI: 1.11-1.69], p=0.004), when controlling for patient, tumor, and facility factors.
Conclusion: Submandibular malignancies have a high rate of positive margins at 41%. Higher T stage and adenoid cystic carcinoma histology were associated with increased risk of positivemargins, and diagnostic biopsies decreased the likelihood of positive margins. Academic centers had lower rates of positive margins. Finally, positive margins were associated with decreased overall survival, even though the majority of patients (77%) received adjuvant therapy after having a positive margin.