National analysis of positive surgical margins in oropharyngeal salivary gland malignancies

Objective: Positive surgical margins (PSM) are associated with worse survival in oropharyngeal salivary gland malignancies (OPSGM), but existing literature is limited to small series. Our objective was to identify risk factors for PSM using the national cancer database (NCDB), including a transoral robotic surgical (TORS) approach. Methods: NCDB was queried for patients with T1-T4a OPSGM undergoing resection between 2010 and 2017. Risk factors for PSM were determined using logistic regression. Overall survival (OS) was analyzed using Kaplan-Meier and Cox proportional hazards models. Results: Of 785 patients, 165 (21.0 %) had PSM. Age, stage T4a tumors (OR 2.00, 95 % Confidence Interval [CI]: 1.03–3.88), adenoid cystic carcinoma (OR 2.02, 95 % CI: 1.29–3.18), and treatment at lower volume institutions (OR 1.68, 95 % CI: 1.09–2.59) were all independently associated with PSM. TORS versus a non-robotic approach was not associated with PSM (23.9 % vs 20.4 %, p 0.358), respectively. Positive margins were independently associated with a worse OS than negative margins (HR 1.63, 95 % CI: 1.03–2.59). Adjuvant radiation therapy was associated with improved survival in high grade tumors with positive margins. Conclusion: This study represents the largest review assessing risk factors for positive margins in OPSGM. Histologic type (adenoid cystic carcinoma), age, T4a tumor stage and treatment at a lower volume institution were all predictive of positive margins. With increasing use of TORS over the last decade, there does not appear to be a greater risk of positive margins using this modality in select patients. Level of evidence: N/A.