Table 2. Associations among the grade of tumor cell differentiation and tumor pathological stage, including overall stage, T stage, N stage, recurrence status, and extranodal spread.

		Grade
		Grade 1 (n = 435)		Grade 2 (n = 1964)		Grade 3 (n = 136)		Total (n = 2535)		p-value
		N	%	N	%	N	%	N	%
Stage	1	249	59.1	712	36.8	27	20.5	988	39.7	<0.001
	2	70	16.6	359	18.6	31	23.5	460	18.5
	3	30	7.1	164	8.5	21	15.9	215	8.6
	4	72	17.1	699	36.1	53	40.2	824	33.1
	Missing data							48
T stage	1	262	60.2	812	41.5	36	26.5	1110	43.9	<0.001
	2	77	17.7	477	24.4	46	33.8	600	23.7
	3	25	5.7	109	5.6	17	12.5	151	6.0
	4	71	16.3	560	28.6	37	27.2	668	26.4
	No residual tumor							6
N stage	0	261	93.9	1096	70.7	59	54.1	1416	73.1	<0.001
	1	10	3.6	154	9.9	18	16.5	182	9.4
	2	7	2.5	273	17.6	29	26.6	309	16.0
	3	0	0.0	27	1.7	3	2.8	30	1.5
	Incomplete data							598
N stage	Negative	261	93.9	1096	70.7	59	54.1	1416	73.1	<0.001
	Positive	17	6.1	454	29.3	50	45.9	521	26.9
	Incomplete data							598
Extra-nodal spread	No	271	97.5	1318	85.0	80	73.4	1669	86.2	<0.001
	Yes	7	2.5	232	15.0	29	26.6	268	13.8
	Incomplete data							598
Recurrence	No	375	86.2	1563	79.4	94	69.1	2028	80.0	<0.001
	Yes	60	13.8	405	20.6	42	30.9	507	20.0

p-value by chi-square test. In the overall stage, N positive or negative group and extra-nodal spread group, p trend < 0.001.

Grade 1: well differentiated; Grade 2: moderately differentiated; Grade 3: poorly differentiated.

In the T stage group, 6 cases received curative chemoradiotherapy first, and the final pathological report showed no residual tumor.

In the overall stage, 48 cases were excluded due to poor data quality.

In the N stage and extranodal spread group, 550 cases were excluded due to operation without neck dissection and 48 cases were excluded due to poor data quality.