Table 1. Baseline characteristics of the initial study cohort stratified by low- and high-risk EC, and the high-risk validation cohort.

	Low risk (n=250)		High risk (n=105)			Validation cohort (n=72)
	Number	% or Inter-quartile range (IQ)	Number	% or Inter-quartile range (IQ)	Difference between low and high risk	Number	% or Inter-quartile range (IQ)
Median age	64	IQ: 56–73	65	IQ: 56–73	chi2; df; P-value	69	IQ: 61–76
Treatment
Surgery	250	100.0	105	100.0	—	72	100.0
Adjuvant radiotherapy	127	50.8	80	76.2	19.6; 1; <0.001	42	56.8
Chemotherapy	5	2.0	4	3.8	1.0; 1; =0.332	13	17.6
FIGO					53.0; 3; <0.001
Stage 1	164	65.6	32	30.5		35	49.3
Stage 2	40	16.0	18	17.1		9	12.6
Stage 3	40	16.0	37	35.2		23	0.32
Stage 4	6	2.4	18	17.1		4	0.1
Missing						1
Invasion myometrium					22.2; 1; <0.001
<half	163	65.2	40	38.1		13	19.7
>half	87	34.8	65	61.9		53	80.3
Missing						6
Lymph nodes (any)					4.9; 1; =0.027
Negative	67	79.8	46	63.9		a	a
Positive	17	20.2	26	36.1		9	12.7
Not assessed	166		33
Lymphovascular invasion					42.3; 1; <0.001
No	194	81.9	48	47.1		23	46.0
Yes	43	18.1	54	52.9		27	54.0
Missing	13		3			22
Differentiation grade					350.2; 3; <0.001
Grade 1	159	63.6				3	6.7
Grade 2	91	36.4	1	1.0		5	11.1
Grade 3			98	93.3		37	82.2
Undifferentiated			6	5.7
Missing						27
Tumour type					136.4; 3; <0.001
Endometrioid	250	100.0	56	53.4		45	68.1
Serous papillary			18	17.1		9	13.6
Clear cell			25	23.8		18	27.3
Undifferentiated			6	5.7		6
HLA class 1b					1.6; 1; =0.212
Normal expression	110	57.9	44	50.0		—	—
Loss of expression	85	42.1	44	50.0		—	—
Missing	48		17
Memory T cellsb					3.7; 1; =0.056
None	69	37.7	41	45.9		38	61.3
Present	130	62.3	47	54.1		24	38.7
Missing	51		17			12
CTLsb					0.6; 1; =0.423
Below median	100	48.0	48	50.7		38	63.3
Above median	112	52.0	44	49.3		22	39.7
Missing	38		13			12
Ratio cytotoxic/regulatory T cellsb					10,0; 1; =0.002
<median	88	44.2	58	61.5		—	—
>median	113	55.8	33	38.5		—	—
Missing	49		14

Abreviations: CTLs=cytotoxic T cells; EC=endometrial cancer; HLA=human leukocyte antigen. Percentages exclude missing values.

^aData on the number of lymph node dissections performed in the validation cohort was unknown.

^bValues before imputation. Relative efficiency of imputation was between 0.97 and 1.00.