Table 1. Patient clinicopathologic characteristics of the training and validation cohorts.

Variable	Training set (n = 797)		Validation set (n = 398)
	No. of Patients	%	No. of Patients	%
Sex
Male	688	86.3	345	86.7
Female	109	13.7	53	13.3
Age (years)
≤50	132	16.6	73	18.3
51–60	317	39.8	154	38.2
61–70	272	34.1	136	34.2
≥71	76	9.5	35	8.8
Mean, Median (Range)	59.03,59.0 (34–80)		58.85,59 (37–97)
Body Mass Index (kg/m 2 )
<18.5	111	13.9	37	9.3
18.50–24.49	606	76.0	321	80.7
≥24.50	80	10.0	40	10.1
Mean, Median (Range)	21.3,21.1 (14–30)		21.4,21.2 (15–31)
Smoking history
No	209	26.2	114	28.6
Yes	588	73.8	284	71.4
Alcohol intake
No	287	36.0	145	36.4
Yes	510	64.0	253	63.6
Tumor location
Upper	21	2.6	7	1.8
Middle	392	49.2	197	49.5
Lower	384	48.2	194	48.7
Tumor length (cm)
<3.0	137	17.2	67	16.8
3.0–4.9	325	40.8	162	40.7
5.0–7.9	292	36.6	148	37.2
≥8	43	5.4	21	5.3
Mean, Median (Range)	4.41,4.0 (0–14)		4.42,4.05 (0–10)
Grade
Well-differentiated	125	15.7	69	17.3
Moderately differentiated	529	66.4	264	66.3
Poorly differentiated	138	17.3	64	16.1
Undifferentiation	5	0.6	1	0.3
Surgical approach
Ivro-Lewis esophagectomy	580	72.8	282	70.9
McKeownesophagectomy	172	21.6	91	22.9
Left transthoracic esophagectomy	45	5.6	25	6.3
Number of examined lymph nodes
<10	42	5.3	25	6.3
10–19	241	30.2	103	25.9
20–29	286	35.9	168	42.2
30–39	151	18.9	69	17.3
40–49	54	6.8	18	4.5
≥50	23	2.9	15	3.8
Mean, Median (Range)	24.81, 23 (3–69)		24.6, 23 (1–62)
Number of positive lymph nodes (N stage)
0 (N0)	435	54.6	208	52.3
1–2 (N1)	190	23.8	99	24.9
3–6 (N2)	123	15.4	62	15.6
≥7 (N3)	49	6.1	29	7.3
Mean, Median (Range)	1.68, 0 (0–29)		1.73, 0 (0–26)
Extent of number of positive lymph nodes (Cervical, upper mediastinal, lower mediastinal and abdomial fields)
0	435	54.6	208		52.3
1 field	209	26.2	114		28.6
2 fields	121	15.2	59		14.8
3 fields	29	3.6	17		4.3
4 fields	3	0.4	0		0
Depth of invasion (T stage)
Epithelial lamina	9	1.1	4	1.0
Lamina propria and muscularis mucosae	27	3.4	17	4.3
Submucosa	94	11.8	40	10.1
Superficial and deep muscular layer	143	17.9	64	16.1
Adventitia	480	60.2	238	59.8
Adjacent structure	44	5.5	35	8.8
Vessel infiltration
No	660	82.8	341	85.7
Yes	137	17.2	57	14.3
TNM staging (6 th edition)
I a	9	1.1	5	1.3
I b	101	12.7	51	12.8
II a	311	39	145	36.40
II b	69	8.7	27	6.8
III	307	38.5	170	42.7
TNM staging (7 th edition)
I a	23	2.9	15	3.8
I b	118	14.8	52	13.1
II a	155	19.4	62	15.6
II b	177	22.2	92	23.1
III a	156	19.6	82	20.6
III b	93	11.7	45	11.3
III c	75	9.4	60	12.6
Overall Survival
3-year survival rate	46%		44%
5-year survival rate	30%		35%
Mean, Median (Range)	30.85, 25.00(1–127)		31.16, 24.50(2–117)