Table 1.

Patient characteristics of the exploratory and independent validation cohort: p values were obtained by using two-sided Mann–Whitney U-tests for continuous variables and ${\chi }^2$ homogeneity tests for categorical variables.

Variable	Exploratory cohort (n = 206)		Independent validation cohort (n = 85)		p value
	Median	(Range)	Median	(Range)
Follow up time of patients alive (months)	52.62	(4.27–131.91)	42.55	(7.85–107.27)	0.72
Age (years)	59.00	(39.20–84.50)	55.00	(37.00–76.00)	0.023
Primary tumour volume (${\text{cm}}^3$)	29.13	(4.52–321.74)	40.62	(2.70–239.07)	0.039

	Number of patients	(%)	Number of patients	(%)
Gender male/female	174/32	(84/16)	74/11	(87/13)	0.70
cT-stage T1/T2/T3/T4	2/23/51/130	(1/11/25/63)	2/9/30/44	(2/11/35/52)	0.21
cN-stage N0/N1/N2/N3/unknown	30/7/154/15/0	(15/3/75/7/0)	9/8/64/3/1	(11/9/75/4/1)	0.097
UICC-stage I/II/III/IV	0/0/15/191	(0/0/7/93)	1/2/9/73	(1/2/11/86)	0.039
Tumour site oropharynx/oral cavity/hypopharynx/larynx	93/51/62/0	(45/25/30/0)	29/23/28/5	(34/27/33/6)	0.003
p16 status negative/positive/unknown	148/28/30	(72/13/15)	52/5/28	(61/6/33)	0.26
Pathological grading 0/1/2/3/unknown	1/6/131/61/7	(1/3/63/30/3)	0/0/43/35/7	(0/0/51/41/8)	0.071
Smoking status no/yes/unknown	41/163/2	(20/79/1)	13/51/21	(15/60/25)	1.00
Alcohol consumption no/yes/unknown	62/85/59	(30/41/29)	23/25/37	(27/29/44)	0.60
Loco-regional tumour recurrence	84	(41)	28	(33)	0.26