Long-term colorectal cancer (CRC) incidence in the low-risk group by baseline characteristics and number of surveillance visits
| N (%) | Person-years | CRC cases | Incidence per 100 000 person-years (95% CI) | Univariable HR (95% CI) | P value | Multivariable HR (95% CI) | P value | |
| Total | 14 401 (100) | 138 903 | 195 | 140 (122 to 162) | – | – | – | – |
| Number of surveillance visits* | – | – | – | – | – | <0.0001 | – | <0.0001 |
| 0 | 7207 (50.1) | 84 591 | 143 | 169 (143 to 199) | 1 | – | 1 | – |
| 1 | 3959 (27.5) | 34 507 | 41 | 119 (87 to 161) | 0.55 (0.39 to 0.79) | – | 0.56 (0.39 to 0.80) | – |
| 2 | 1943 (13.5) | 12 986 | 8 | 62 (31 to 123) | 0.26 (0.12 to 0.54) | – | 0.27 (0.13 to 0.56) | – |
| ≥3 | 1292 (9.0) | 6818 | 3 | 44 (14 to 136) | 0.17 (0.05 to 0.57) | – | 0.18 (0.05 to 0.58) | – |
| Sex | – | – | – | – | – | 0.67 | – | 0.99 |
| Women | 6382 (44.3) | 63 337 | 92 | 145 (118 to 178) | 1 | – | 1 | – |
| Men | 8019 (55.7) | 75 567 | 103 | 136 (112 to 165) | 0.94 (0.71 to 1.25) | – | 1.00 (0.75 to 1.32) | – |
| Age, years | – | – | – | – | – | <0.0001 | – | <0.0001 |
| <55 | 3569 (24.8) | 40 422 | 21 | 52 (34 to 80) | 1 | – | 1 | – |
| 55–64 | 3991 (27.7) | 42 121 | 46 | 109 (82 to 146) | 2.12 (1.26 to 3.55) | – | 2.05 (1.22 to 3.44) | – |
| 65–74 | 4258 (29.6) | 38 799 | 76 | 196 (156 to 245) | 3.87 (2.38 to 6.28) | – | 3.52 (2.17 to 5.73) | – |
| ≥75 | 2583 (17.9) | 17 561 | 52 | 296 (226 to 389) | 6.12 (3.67 to 10.20) | – | 5.02 (3.00 to 8.39) | – |
| Number of adenomas | – | – | – | – | – | 0.30 | – | 0.69 |
| 1 | 11 762 (81.7) | 113 729 | 154 | 135 (116 to 159) | 1 | – | 1 | – |
| 2 | 2639 (18.3) | 25 175 | 41 | 163 (120 to 221) | 1.20 (0.85 to 1.70) | – | 1.07 (0.76 to 1.53) | – |
| Adenoma histology† | – | – | – | – | – | 0.0093 | – | 0.0067 |
| Tubular | 11 138 (77.3) | 107 018 | 132 | 123 (104 to 146) | 1 | – | 1 | – |
| Tubulovillous | 2113 (14.7) | 20 130 | 44 | 219 (163 to 294) | 1.69 (1.21 to 2.37) | – | 1.71 (1.21 to 2.40) | – |
| Villous | 190 (1.3) | 1906 | 2 | 105 (26 to 420) | – | – | ||
| Unknown | 960 (6.7) | 9849 | 17 | 173 (107 to 278) | 1.39 (0.84 to 2.30) | – | 1.52 (0.92 to 2.52) | – |
| Adenoma dysplasia† | – | – | – | – | – | 0.0543 | – | 0.0775 |
| Low-grade | 13 242 (92.0) | 125 812 | 171 | 136 (117 to 158) | 1 | – | 1 | – |
| High-grade | 357 (2.5) | 3469 | 11 | 317 (176 to 573) | 2.32 (1.26 to 4.28) | – | 2.20 (1.18 to 4.10) | – |
| Unknown | 802 (5.6) | 9623 | 13 | 135 (78 to 233) | 0.99 (0.56 to 1.74) | – | 0.93 (0.52 to 1.66) | – |
| Proximal polyps | – | – | – | – | – | 0.0046 | – | 0.002 |
| No | 8133 (56.5) | 80 118 | 93 | 116 (95 to 142) | 1 | – | 1 | – |
| Yes | 6268 (43.5) | 58 785 | 102 | 174 (143 to 211) | 1.50 (1.13 to 1.99) | – | 1.57 (1.18 to 2.10) | – |
| Completeness of colonoscopy | – | – | – | – | – | 0.17 | – | 0.0274 |
| Complete | 11 719 (81.4) | 108 319 | 144 | 133 (113 to 157) | 1 | – | 1 | – |
| Incomplete | 1140 (7.9) | 10 674 | 26 | 244 (166 to 358) | 1.26 (0.91 to 1.74) | – | 1.47 (1.05 to 2.04) | – |
| Unknown | 1542 (10.7) | 19 910 | 25 | 126 (85 to 186) | – | – | ||
| Bowel preparation quality | – | – | – | – | – | 0.15 | – | 0.32 |
| Excellent or good | 5145 (35.7) | 52 129 | 84 | 161 (130 to 200) | 1 | – | 1 | – |
| Satisfactory | 2540 (17.6) | 22 051 | 30 | 136 (95 to 195) | 0.85 (0.56 to 1.29) | – | 0.81 (0.53 to 1.23) | – |
| Poor | 968 (6.7) | 7970 | 15 | 188 (113 to 312) | 1.18 (0.68 to 2.04) | – | 1.09 (0.63 to 1.88) | – |
| Unknown | 5748 (39.9) | 56 754 | 66 | 116 (91 to 148) | 0.72 (0.52 to 1.00) | – | 0.76 (0.55 to 1.05) | – |
| Year of baseline visit | – | – | – | – | – | 0.71 | – | 0.45 |
| 1984–1994 | 1640 (11.4) | 23 185 | 32 | 138 (98 to 195) | 1 | – | 1 | – |
| 2000–2004 | 5168 (35.9) | 56 134 | 86 | 153 (124 to 189) | 1.06 (0.69 to 1.62) | – | 0.93 (0.60 to 1.43) | – |
| 2005–2010 | 7593 (52.7) | 59 585 | 77 | 129 (103 to 162) | 0.92 (0.59 to 1.44) | – | 0.77 (0.48 to 1.23) | – |
| Length of baseline visit | – | – | – | – | – | 0.74 | – | 0.64 |
| 1 day | 11 354 (78.8) | 110 143 | 152 | 138 (118 to 162) | 1 | – | 1 | – |
| 2 days–3 months | 1373 (9.5) | 12 314 | 19 | 154 (98 to 242) | 1.12 (0.70 to 1.81) | – | 1.13 (0.70 to 1.84) | – |
| 3–6 months | 950 (6.6) | 9309 | 16 | 172 (105 to 281) | 1.24 (0.74 to 2.07) | – | 1.39 (0.82 to 2.33) | – |
| ≥6 months | 724 (5.0) | 7137 | 8 | 112 (56 to 224) | 0.81 (0.40 to 1.65) | – | 0.91 (0.45 to 1.87) | – |
The final multivariable model contained number of surveillance visits, age, adenoma histology, proximal polyps and completeness of colonoscopy. For these variables, the multivariable HRs were from the final multivariable model and the p values were for inclusion of the variable in the model, calculated with the likelihood ratio test. For the remaining variables, the multivariable HRs were for if the variable was added as an additional variable to the final multivariable model.
*The number of surveillance visits was included as a time-varying covariate; patients who attended any surveillance contributed person-years to more than one category of number of surveillance visits.
†Adenoma histology and dysplasia were defined according to the worst histology (greatest degree of villousness) and worst dysplasia (highest grade) seen at baseline, respectively.