Table 6. Comparison and validation between the two formulas.

	Current formula		Previous formula		P value
	C-index	AIC	C-index	AIC
Training group
V stage	0.715	3768.2	0.693	3845.4	< 0.001
VNM stage	0.756	3667.2	0.732	3753.3	< 0.001
Multivariable model	0.775	3635.6	0.764	3712.6	< 0.001
Validation group
V stage	0.701	3962.4	0.684	3993.3	< 0.001
VNM stage	0.746	3862.9	0.723	3917.5	< 0.001
Multivariable model	0.769	3848.4	0.756	3908.2	< 0.001

Current formula: V = Tumor diameter × (T stage)²/2;

Previous formula [33]: V = pT × (tumor size/2)².