Table 2. Observed and expected number of rectal cancers and corresponding standardised incidence ratios in patients with irritable bowel syndrome overall and according to period of follow-up, gender, age at diagnosis and calendar period of diagnosis.

	All 57 851 IBS patients			19 150 IBS patients with known colonoscopya
	Observed cancers, N	Expected cancers, N	SIR (95% CI)	Observed cancers, N	Expected cancers, N	SIR (95% CI)
Total	115	171.0	0.67 (0.52–0.85)	27	27.3	0.99 (0.65–1.44)
Follow-up
⩽3 months	18	3.7	4.81 (2.85–7.60)	13	1.2	10.86 (5.78–18.58)
4–12 months	14	11.2	1.25 (0.68–2.09)	4	3.5	1.13 (0.31–2.90)
2nd and 3rd year	14	28.2	0.50 (0.27–0.83)	3	8.3	0.36 (0.07–1.05)
4th and 5th year	19	24.7	0.77 (0.46–1.20)	4	6.3	0.63 (0.17–1.62)
6th to 10th year	15	45.6	0.33 (0.18–0.54)	3	7.1	0.42 (0.09–1.23)
>10 years	35	57.5	0.61 (0.42–0.85)	0	0.8	—
Gender
Women	71	102.7	0.69 (0.54–0.87)	12	14.6	0.82 (0.43–1.44)
Men	44	68.3	0.64 (0.47–0.86)	15	12.8	1.17 (0.66–1.94)
Age
<20 years	0	0.2	—	0	0	—
20–39 years	6	9.6	0.62 (0.23–1.36)	1	0.5	1.85 (0.05–10.32)
40–49 years	14	20.7	0.68 (0.37–1.13)	3	2.1	1.40 (0.29–4.08)
50–59 years	26	41.9	0.62 (0.40–0.91)	2	6.8	0.29 (0.04–1.06)
60–69 years	30	50.2	0.60 (0.40–0.85)	13	9.0	1.45 (0.77–2.48)
70–79 years	24	37.6	0.64 (0.41–0.95)	3	6.7	0.45 (0.09–1.31)
⩾80 years	15	10.9	1.38 (0.77–2.28)	5	2.2	2.30 (0.75–5.36)

Abbreviations: IBS=irritable bowel syndrome; CI=confidence interval; SIR=standardised incidence ratio.

^aColonoscopy or flexible sigmoidoscopy.