Table 1.
Long-term incidence of colorectal cancer by number of surveillance visits and baseline characteristics (n=21 318)
| 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* | |
| Total | 21 318 | 100 | 210 814 | 368 | 175 (158 to 193) | ||||
| No of surveillance visits‡ | <0.001 | <0.001 | |||||||
| 0 | 9714 | 45.6 | 116 248 | 214 | 184 (161 to 210) | 1 | 1 | ||
| 1 | 5903 | 27.7 | 56 923 | 96 | 169 (138 to 206) | 0.72 (0.56 to 0.92) | 0.65 (0.50 to 0.84) | ||
| 2 | 3515 | 16.5 | 25 058 | 32 | 128 (90 to 181) | 0.49 (0.33 to 0.71) | 0.43 (0.29 to 0.63) | ||
| ≥3 | 2186 | 10.3 | 12 586 | 26 | 207 (141 to 303) | 0.66 (0.43 to 1.03) | 0.54 (0.35 to 0.85) | ||
| Sex | 0.93 | 0.90 | |||||||
| Women | 9022 | 42.3 | 92 173 | 161 | 175 (150 to 204) | 1 | 1 | ||
| Men | 12 296 | 57.7 | 118 641 | 207 | 174 (152 to 200) | 1.01 (0.82 to 1.24) | 1.01 (0.82 to 1.25) | ||
| Age at baseline, years | <0.001 | <0.001 | |||||||
| <55 | 4298 | 20.2 | 51 463 | 36 | 70 (50 to 97) | 1 | 1 | ||
| 55–64 | 5956 | 27.9 | 64 938 | 77 | 119 (95 to 148) | 1.75 (1.18 to 2.60) | 1.61 (1.08 to 2.40) | ||
| 65–74 | 6894 | 32.3 | 65 186 | 158 | 242 (207 to 283) | 3.78 (2.63 to 5.44) | 3.27 (2.27 to 4.72) | ||
| ≥75 | 4170 | 19.6 | 29 228 | 97 | 332 (272 to 405) | 5.66 (3.84 to 8.34) | 4.31 (2.91 to 6.38) | ||
| No of PMPs | <0.001 | 0.003 | |||||||
| 1 | 12 231 | 57.4 | 124 117 | 163 | 131 (113 to 153) | 1 | 1 | ||
| 2 | 4714 | 22.1 | 45 601 | 100 | 219 (180 to 267) | 1.70 (1.33 to 2.18) | 1.36 (1.07 to 1.71) | ||
| 3 | 2035 | 9.6 | 19 482 | 41 | 210 (155 to 286) | 1.63 (1.16 to 2.30) | |||
| 4 | 951 | 4.5 | 8856 | 23 | 260 (173 to 391) | 2.02 (1.31 to 3.13) | |||
| ≥5 | 1387 | 6.5 | 12 760 | 41 | 321 (237 to 436) | 2.53 (1.79 to 3.56) | 1.82 (1.25 to 2.66) | ||
| PMP size, mm§ | <0.001 | 0.46 | |||||||
| <10 | 11 553 | 54.2 | 116 281 | 166 | 143 (123 to 166) | 1 | 1 | ||
| 10–19 | 6081 | 28.5 | 59 382 | 109 | 184 (152 to 221) | 1.29 (1.01 to 1.64) | 1.06 (0.81 to 1.38) | ||
| ≥20 | 3625 | 17.0 | 34 544 | 92 | 266 (217 to 327) | 1.87 (1.45 to 2.42) | 1.28 (0.93 to 1.76) | ||
| Unknown | 59 | 0.3 | 607 | 1 | 165 (23 to 1169) | 1.11 (0.16 to 7.92) | 0.69 (0.10 to 5.03) | ||
| Adenoma histology¶ | <0.001 | <0.001 | |||||||
| Tubular | 12 786 | 60.0 | 127 882 | 171 | 134 (115 to 155) | 1 | 1 | ||
| Tubulovillous | 6480 | 30.4 | 62 187 | 137 | 220 (186 to 260) | 1.66 (1.33 to 2.08) | 1.42 (1.12 to 1.80) | ||
| Villous | 1045 | 4.9 | 9958 | 31 | 311 (219 to 443) | 2.35 (1.61 to 3.45) | 1.60 (1.07 to 2.40) | ||
| Unknown | 1007 | 4.7 | 10 787 | 29 | 269 (187 to 387) | 1.94 (1.31 to 2.88) | 2.06 (1.37 to 3.11) | ||
| Adenoma dysplasia** | <0.001 | 0.03 | |||||||
| Low grade | 18 592 | 87.2 | 183 696 | 290 | 158 (141 to 177) | 1 | 1 | ||
| High grade | 2148 | 10.1 | 19 913 | 63 | 316 (247 to 405) | 2.03 (1.54 to 2.66) | 1.51 (1.12 to 2.02) | ||
| Unknown | 578 | 2.7 | 7206 | 15 | 208 (125 to 345) | 1.22 (0.72 to 2.06) | 1.22 (0.71 to 2.11) | ||
| Proximal polyps†† | <0.001 | <0.001 | |||||||
| No | 11 566 | 54.3 | 118 513 | 152 | 128 (109 to 150) | 1 | 1 | ||
| Yes | 9752 | 45.8 | 92 301 | 216 | 234 (205 to 267) | 1.86 (1.51 to 2.29) | 1.63 (1.30 to 2.05) | ||
| Year of baseline visit | 0.81 | 0.34 | |||||||
| 1984–1999 | 2057 | 9.7 | 28 319 | 60 | 212 (165 to 273) | 1 | 1 | ||
| 2000–2004 | 6651 | 31.2 | 74 494 | 137 | 184 (156 to 217) | 0.96 (0.69 to 1.34) | 0.89 (0.64 to 1.23) | ||
| 2005–2010 | 12 610 | 59.2 | 108 001 | 171 | 158 (136 to 184) | 0.91 (0.65 to 1.27) | 0.78 (0.56 to 1.10) | ||
| Length of baseline visit, days | <0.001 | 0.04 | |||||||
| 1 | 14 223 | 66.7 | 140 884 | 208 | 148 (129 to 169) | 1 | 1 | ||
| 2–90 | 3035 | 14.2 | 29 429 | 70 | 238 (188 to 301) | 1.63 (1.24 to 2.13) | 1.50 (1.13 to 1.99) | ||
| 91–183 | 2085 | 9.8 | 21 071 | 43 | 204 (151 to 275) | 1.38 (0.99 to 1.92) | 1.21 (0.86 to 1.71) | ||
| ≥184 | 1975 | 9.3 | 19 430 | 47 | 242 (182 to 322) | 1.63 (1.19 to 2.24) | 1.30 (0.92 to 1.82) | ||
| Family history of cancer/CRC‡‡ | 0.22 | 0.10 | |||||||
| No | 19 730 | 92.6 | 191 764 | 340 | 177 (159 to 197) | 1 | 1 | ||
| Yes | 1588 | 7.5 | 19 051 | 28 | 147 (101 to 213) | 0.79 (0.54 to 1.16) | 1.42 (0.95 to 2.11) | ||
*P values were calculated with the likelihood ratio test.
†The final multivariable model contained number of surveillance visits, age, number of PMPs, adenoma histology, adenoma dysplasia, proximal polyps and length of baseline visit. 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. For the remaining variables, the multivariable HRs were for if the variable was added as an additional variable to the final multivariable model.
‡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.
§PMP size was defined according to the largest PMP seen at baseline.
¶Adenoma histology was defined according to the greatest degree of villousness seen at baseline.
**Adenoma dysplasia was defined according to the highest grade of dysplasia seen at baseline.
††Proximal polyps were defined as those proximal to the descending colon.
‡‡Family history of cancer/CRC was defined as ‘family history of cancer or CRC reported at an examination before or during visit’. Of cases with a ‘family history of cancer’, 72% were from a specialist hospital for colorectal diseases and so we assumed these cases had a family history of CRC.
CRC, colorectal cancer; mm, millimetre; PMP, premalignant polyp.