Table S2. Comparison of C-indexes between the nomograms, TNM and SEER stages in EOGC patients.

Survival types	Tumor stage types	Training set				Validation set
		HR	95% CI	P value		HR	95% CI	P value
OS	Nomogram	0.688	0.629–0.747			0.633	0.579–0.687
	SEER stage	0.708	0.659–0.757	0.267		0.685	0.642–0.728	0.198
	TNM 7th stage	0.769	0.717–0.821	0.007		0.750	0.707–0.793	<0.001
CSS	Nomogram	0.785	0.735–0.835			0.733	0.686–0.780
	SEER stage	0.726	0.680–0.772	0.035		0.690	0.646–0.734	0.033
	TNM 7th stage	0.782	0.732–0.832	0.457		0.762	0.719–0.805	0.366

TNM, tumor-node-metastasis; SEER, surveillance, epidemiology and end results; EOGC, early-onset gastric cancer; C-index, concordance index; HR, hazard ratio; CI, confidence intervals; OS, overall survival; CSS, cancer-specific survival.