Table 3. Cox regression model for the independent prognostic significance of necrosis in the validation cohort.

	DFS			CSS			OS
	HR	95% CI	P-value	HR	95% CI	P-value	HR	95% CI	P-value
Age (<65 vs ⩾65)	—	—	—	—	—	—	1.87	1.34–2.61	2.6E−4
Tumour invasion (T1–T2 vs T3–T4)	1.19	0.66–2.15	0.559	1.30	0.71–2.38	0.396	0.74	0.47–1.15	0.181
Nodal metastases (N0 vs N1-N2)	1.25	0.77–2.02	0.367	1.88	1.22–2.88	4.1E−3	1.44	1.00–2.06	0.050
Distant metastases (M0 vs M1)	—	—	—	4.95	3.16–7.73	2.7E−12	3.36	2.20–5.14	2.1E−8
WHO Grade (1–2 vs 3)	—	—	—	1.82	1.20–2.76	5.2E−3	1.51	1.04–2.19	0.031
Tumour location (Colon vs Rectum)	1.84	1.21–2.79	4.4E−3	1.78	1.22–2.59	2.5E−3	1.49	1.09–2.04	0.013
Serrated growth pattern (No vs Yes)	0.97	0.44–2.14	0.941	1.27	0.69–2.31	0.442	1.32	0.81–2.14	0.263
Lymphatic or blood vessel invasion (No vs Yes)	1.76	1.07–2.90	0.025	1.80	1.18–2.74	6.2E−3	1.83	1.28–2.62	9.8E−4
Infiltrative tumour border (No vs Yes)	3.50	2.08–5.91	2.6E−6	2.57	1.73–3.84	3.6E−6	2.44	1.70–3.51	1.5E−6
Tumour necrosis (<10% vs ⩾10%)	1.60	1.05–2.46	0.031	1.84	1.27–2.67	1.3E−3	1.51	1.10–2.06	0.010

Abbreviations: CI=confidence interval; CSS=cancer-specific survival; DFS=disease-free survival; HR=hazard ratio; OS=overall survival; RT/CRT=radiotherapy/chemoradiotherapy; TNM=tumour, node and metastasis.

All the models included TNM stage variables, serrated histology, and tumour necrosis. Other variables were selected utilising the stepwise forward selection method based on their significance in the model.