Table 3

Effects of surveillance on colorectal cancer incidence by number of surveillance visits and risk group

	n	%	No of person-years	No of CRCs	Incidence rate per 100 000 person-years (95% CI)	Effect of surveillance on CRC incidence*
	n	%	No of person-years	No of CRCs	Incidence rate per 100 000 person-years (95% CI)	Univariable HR (95% CI)	P value†	Multivariable HR (95% CI)‡	P value†
Low-risk patients§							<0.001		0.001
0 visit	7438	49.3	90 451	136	150 (127 to 178)	1		1
1 visit	4199	27.8	39 392	44	112 (83 to 150)	0.57 (0.40 to 0.81)		0.58 (0.41 to 0.83)
≥2 visits	3442	22.8	22 654	26	115 (78 to 169)	0.48 (0.30 to 0.75)		0.53 (0.33 to 0.83)
Total	15 079	70.7	152 497	206	135 (118 to 155)
High-risk patients§							<0.001		0.002
0 visit	2276	36.5	25 796	78	302 (242 to 377)	1		1
1 visit	1704	27.3	17 531	52	297 (226 to 389)	0.73 (0.51 to 1.05)		0.71 (0.49 to 1.03)
≥2 visits	2259	36.2	14 990	32	213 (151 to 302)	0.42 (0.27 to 0.66)		0.44 (0.28 to 0.70)
Total	6239	29.3	58 318	162	278 (238 to 324)

*Number of surveillance visits was included as a time-varying covariate, meaning that patients who had surveillance contributed person-years to more than a single category of number of surveillance visits.
†P values were calculated with the likelihood ratio test.
‡Multivariable HR adjusted for age, number of premalignant polyps, adenoma histology, adenoma dysplasia, proximal polyps and length of baseline visit, the characteristics independently associated with CRC incidence in the whole cohort.
§High-risk patients were those with ≥2 premalignant polyps, of which ≥1 was advanced, ≥5 premalignant polyps, or ≥1 large (≥20 mm) non-pedunculated premalignant polyp; low-risk patients had none of these findings.
CRC, colorectal cancer.