Positive surgical margins in parotid malignancies: Institutional variation and survival association

Objectives/hypothesis: To establish benchmarks for positive margin incidence in parotid cancers, associate positive margin status with patient, tumor, and institutional factors and overall survival, and characterize institutional variation in positive margin incidence.

Study design: Retrospective database analysis.

Methods: We identified patients surgically treated for a parotid malignancy 2004 to 2013 in the National Cancer Database. We associated positive margins with patient, tumor, and treatment factors by multivariable logistic regression and with overall survival by Cox proportional hazards regression. We characterized institutional variation in positive margin rates by facility type and volume.

Results: A total of 5,639 patients were identified. The overall positive margin rate was 31%. By institution, positive margin rates varied from 0% to 100%, with a median rate of 31% (interquartile range = 18%-43%). Adenoid cystic carcinoma was associated with increased, and low-grade mucoepidermoid carcinoma with decreased, odds of positive margins, (odds ratio [OR] = 1.91 [95% confidence interval {CI}: 1.54-2.38], P < .001 and OR = 0.68 [95% CI: 0.53-0.87], P = .002, respectively). Treatment at academic or high-volume facilities was associated with decreased odds of positive margins (OR = 0.79 [95% CI: 0.68-0.91], P = .001 and OR = 0.76 [95% CI: 0.63-0.91], P = .004). Positive surgical margins were associated with decreased overall survival (62% vs. 79% 5-year overall survival, hazard ratio [HR] = 1.34 [95% CI: 1.20-1.49], P < .001). Upon stratification by histology, this association was maintained for high-grade, but not low-grade, mucoepidermoid carcinoma (52% vs. 74%, HR = 1.56 [95% CI: 1.31-1.86], P < .001 and 89% versus 91%, HR = 1.05 [95% CI: 0.60-1.83], P = .874, respectively).

Conclusions: Tumor and institutional factors are associated with positive surgical margins. Positive margin rates vary substantially between facilities and are less likely at academic and high-volume facilities. Positive surgical margins are associated with decreased overall survival and could be considered quality indicators in parotid malignancies.

Level of evidence: 2c Laryngoscope, 129:129-137, 2019.