Table 5. Survival of patients stratified by stages according to lymphadenectomy and chemotherapy in overall population (N = 5982).

	Ngroup 1	5-y OSgroup 1	Ngroup 2	5-y OSgroup 2	P value†	Unadjusted HR (95% CI)	P value	Adjusted HR (95% CI)*	P value	Adjusted HR (95% CI)* for patients with R0 resection	P value
Without chemotherapy (Group 1) VS with chemotherapy (Group 2)
I	3065	94.7%	84	90.4%	0.162	1.60 [0.82–3.11]	0.165	1.22 [0.54–2.71]	0.635	1.34 [0.60–2.96]	0.474
II	419	76.4%	569	78.6%	0.404	0.89 [0.68–1.17]	0.405	0.84 [0.62–1.14]	0.255	0.83 [0.61–1.12]	0.226
III	438	40.2%	1154	51.8%	< 0.001	0.70 [0.60–0.81]	< 0.001	0.69 [0.59–0.81]	< 0.001	0.68 [0.57–0.80]	< 0.001
IV	67	7.3%	186	22.4%	0.001	0.62 [0.45–0.84]	0.002	0.60 [0.42–0.86]	0.006	0.33 [0.13–0.87]	0.025
Group 1 VS Group 2 in D2/D2+ lymphadenectomy group
I	993	94.3%	38	92.0%	0.983	1.01 [0.31–3.28]	0.983	1.21 [0.29–5.00]	0.794	1.21 [0.29–5.00]	0.794
II	304	80.5%	415	78.5%	0.531	1.12 [0.79–1.57]	0.532	1.05 [0.71–1.55]	0.814	1.06 [0.72–1.56]	0.785
III	266	46.4%	947	53.9%	0.007	0.78 [0.64–0.94]	0.008	0.70 [0.57–0.86]	0.001	0.69 [0.56–0.85]	< 0.001
IV	33	3.0%	130	21.5%	0.003	0.55 [0.37–0.83]	0.004	0.53 [0.31–0.91]	0.021	–#	–#
Group 1 VS Group 2 in D1/D1+ lymphadenectomy group
I	2072	95.0%	46	89.0%	0.060	2.14 [0.95–4.79]	0.065	1.40 [0.51–3.87]	0.515	1.42 [0.52–3.93]	0.497
II	115	65.6%	154	79.0%	0.010	0.53 [0.33–0.87]	0.011	0.51 [0.30–0.89]	0.018	0.51 [0.30–0.89]	0.018
III	172	30.6%	207	42.7%	0.001	0.67 [0.52–0.86]	0.002	0.60 [0.45–0.80]	< 0.001	0.60 [0.45–0.82]	0.001
IV	34	11.4%	56	24.0%	0.044	0.62 [0.38–0.99]	0.047	0.43 [0.24–0.78]	0.005	–#	–#
D1/D1+ (Group 1) VS D2/D2+ lymphadenectomy (Group 2)
I	2118	94.8%	1031	94.2%	0.323	1.18 [0.85–1.62]	0.324	0.94 [0.66–1.34]	0.720	0.98 [0.68–1.39]	0.888
II	269	73.3%	719	79.1%	0.186	0.80 [0.60–1.08]	0.146	0.78 [0.56–1.10]	0.160	0.76 [0.54–1.07]	0.118
III	379	37.2%	1213	52.2%	< 0.001	0.70 [0.60–0.81]	< 0.001	0.79 [0.66–0.95]	0.014	0.81 [0.67–0.99]	0.040
IV	90	19.3%	163	17.8%	0.283	1.17 [0.88–1.56]	0.288	1.39 [0.98–1.97]	0.066	2.64 [0.96–7.26]	0.060
Group 1 VS Group 2 in with chemotherapy group
I	46	89.0%	38	92.0%	0.231	0.44 [0.11–1.74]	0.243	0.16 [0.015–1.68]	0.127	0.16 [0.015–1.68]	0.127
II	154	79.0%	415	78.5%	0.535	1.14 [0.75–1.75]	0.535	1.07 [0.65–1.77]	0.787	1.05 [0.64–1.74]	0.837
III	207	42.7%	947	53.9%	0.022	0.79 [0.64–0.97]	0.023	0.73 [0.57–0.93]	0.011	0.74 [0.57–0.97]	0.025
IV	56	24.0%	130	21.5%	0.291	1.22 [0.84–1.75]	0.296	1.07 [0.68–1.69]	0.763	–#	–#
Group 1 VS Group 2 in without chemotherapy group
I	2072	95.0%	993	94.3%	0.196	1.24 [0.89–1.72]	0.197	0.95 [0.66–1.37]	0.786	0.98 [0.68–1.41]	0.900
II	115	65.6%	304	80.5%	0.004	0.54 [0.35–0.81]	0.003	0.56 [0.34–0.93]	0.023	0.56 [0.34–0.93]	0.023
III	172	30.6%	266	46.4%	0.002	0.69 [0.54–0.88]	0.002	0.67 [0.48–0.93]	0.016	0.69 [0.50–0.95]	0.025
IV	34	11.4%	33	3.0%	0.068	1.59 [0.96–2.64]	0.074	1.79 [0.96–3.34]	0.069	–#	–#

Abbreviations: N, number; OS, overall survival; HR, hazard ratio.

Note: The values of group 1 were regarded as references for the HR analyses.

^†p-value for log-rank test.

^*Adjust for country, gender, age, surgical methods, tumor location, differentiation, tumor size, T stage, N stage, resection type, lymphadenectomy, radicality of surgery, chemotherapy.

^#The valid sample size is too small to calculate the adjust HR.