Table 4

Incidence of colorectal cancer (CRC) and unadjusted effect of surveillance on CRC incidence by number of surveillance visits

n (%)Person-yearsCRC casesIncidence per 100 000 person-years (95% CI)Effect of surveillance*
Univariable HR (95% CI)P value
Low-risk group
 Whole risk group<0.0001
  0 visits7207 (50.1)84 591143169 (143 to 199)1
  1 visit3959 (27.5)34 50741119 (87 to 161)0.55 (0.39 to 0.79)
  ≥2 visits3235 (22.5)19 8051156 (31 to 100)0.23 (0.12 to 0.44)
  Total14 401 (100)138 903195140 (122 to 162)
 Lower-risk subgroup†0.15
  0 visits2804 (53.6)32 9033194 (66 to 134)1
  1 visit1432 (27.4)11 410870 (35 to 140)0.54 (0.25 to 1.20)
  ≥2 visits999 (19.1)5472355 (18 to 170)0.42 (0.12 to 1.48)
  Total5235 (36.4)49 7854284 (62 to 114)
 Higher-risk subgroup†<0.0001
  0 visits4403 (48.0)51 688112217 (180 to 261)1
  1 visit2527 (27.6)23 09733143 (102 to 201)0.52 (0.35 to 0.78)
  ≥2 visits2236 (24.4)14 332856 (28 to 112)0.18 (0.08 to 0.37)
  Total9166 (63.6)89 118153172 (147 to 201)
Intermediate -risk group
 Whole risk group0.0001
  0 visits4683 (39.5)53 927135250 (211 to 296)1
  1 visit3343 (28.2)33 28462186 (145 to 239)0.58 (0.42 to 0.79)
  ≥2 visits3826 (32.3)24 05949204 (154 to 269)0.50 (0.34 to 0.73)
  Total11 852 (100)111 270246221 (195 to 251)
 Lower-risk subgroup‡0.30
  0 visits1932 (40.8)23 23733142 (101 to 200)1
  1 visit1387 (29.3)13 15116122 (75 to 199)0.66 (0.35 to 1.23)
  ≥2 visits1419 (30.0)808213161 (93 to 277)0.63 (0.31 to 1.29)
  Total4738 (40.0)44 47062139 (109 to 179)
 Higher-risk subgroup‡0.0001
  0 visits2751 (38.7)30 690102332 (274 to 404)1
  1 visit1956 (27.5)20 13346228 (171 to 305)0.53 (0.37 to 0.76)
  ≥2 visits2407 (33.8)15 97736225 (163 to 312)0.42 (0.27 to 0.65)
  Total7114 (60.0)66 800184275 (238 to 318)
High-risk group
 Whole risk group0.0006
  0 visits911 (33.5)924344476 (354 to 640)1
  1 visit695 (25.6)714424336 (225 to 501)0.51 (0.30 to 0.85)
  ≥2 visits1113 (40.9)657416243 (149 to 397)0.32 (0.17 to 0.60)
  Total2719 (100)22 96184366 (295 to 453)
 Lower-risk subgroup§0.26
  0 visits606 (33.4)622617273 (170 to 439)1
  1 visit474 (26.1)476612252 (143 to 443)0.66 (0.31 to 1.41)
  ≥2 visits737 (40.6)40399223 (116 to 428)0.49 (0.20 to 1.18)
  Total1817 (66.8)15 03238253 (184 to 347)
 Higher-risk subgroup§0.0006
  0 visits305 (33.8)301727895 (614 to 1305)1
  1 visit221 (24.5)237812505 (287 to 889)0.41 (0.20 to 0.82)
  ≥2 visits376 (41.7)25357276 (132 to 579)0.21 (0.08 to 0.51)
  Total902 (33.2)792946580 (435 to 775)
  • P values calculated with the likelihood ratio test.

  • *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.

  • †The higher-risk subgroup included patients with an incomplete colonoscopy or colonoscopy of unknown completeness, a tubulovillous or villous adenoma, or proximal polyps at baseline; the lower-risk subgroup included patients with none of these factors.

  • ‡The higher-risk subgroup included patients with an incomplete colonoscopy or colonoscopy of unknown completeness, an adenoma with high-grade dysplasia or proximal polyps at baseline; the lower-risk subgroup included patients with none of these factors.

  • §The higher-risk subgroup included patients with an incomplete colonoscopy or colonoscopy of unknown completeness or an adenoma with high-grade dysplasia at baseline; the lower-risk subgroup included patients with none of these factors.