TABLE 3.

Multivariable overall survival model (N = 1335)

Variable	HR (95% CI)	P value
Age at diagnosis	1.04 (1.03–1.05)	<.001
Tumor size in mm (ref: <10)		<.001
10–19	1.46 (0.85–2.49)
20–29	1.34 (0.78–2.33)
30–39	2.25 (1.32–3.84)
40–49	1.96 (1.13–3.39)
≥50	2.92 (1.67–5.13)
Grade (ref: low)		.04
Intermediate	0.97 (0.79–1.20)
High	1.31 (0.97–1.77)
T-stage 3 or 4	1.01 (0.75–1.35)	.94
Positive surgical margin	1.56 (1.29–1.88)	<.001
Lymphovascular invasion	1.05 (0.84–1.31)	.65
N-stage 2 or 3	1.96 (1.54–2.50)	<.001
Level IV or V nodal metastasis	1.80 (1.25–2.57)	.001
Extranodal extension	1.44 (1.08–1.92)	.01
PORT	0.78 (0.64–0.94)	.01
Chemotherapy	1.11 (0.84–1.46)	.47

Notes: Hazard ratios (HR), confidence intervals (CI), and P values are from Cox proportional hazards models. A robust sandwich covariance estimator was used to account for correlation of patients treated at the same facility. The multivariable model was adjusted for diagnosis year (P = .27), gender (P = .21), comorbidity score (P = .10), race (P = .90), income (P = .68), insurance (P = .46), education (P = .68), facility type (P = .63), facility location (P = .75), and great circle distance (P = .02). Postoperative radiotherapy (PORT) and chemotherapy were assessed as time-varying.