Table 2. Multivariable Cox proportional hazards models.

	HR	95% CI	P-value	C-index (%)
Model 1
SSIGN score	1.69	1.39–2.06	<0.0001	92.5
20S proteasome continuous	1.17	1.06–1.28	0.0015
Model 2
SSIGN score	1.60	1.33–1.92	<0.0001	93.2
20S proteasome categorical	4.03	1.55–10.44	0.0041

Abbreviations: CI=confidence intervals; C-index=concordance index; HR=hazards ratio; SSIGN=T, N, M stage, size, grade, and necrosis.

The models included SSIGN score and 20S proteasome serum level as continuous (model 1) or categorical variable (model 2). In both models, 20S proteasome serum levels were retained as independent prognostic factor. The C-index increased significantly from 91.4 to 92.5% and 93.2%, respectively, after the 20S proteasome serum level was introduced in the model.