Table 2.
Cancer Incidence in Danish Same-Sex Twins Born in 1900–1918 and Stratified for Age at Death of Cotwin; Analyses of Subpopulations of One Randomly Selected Twin From Each Twin Pair
| Gender | Lifespan of Cotwin | Observed Number of Cancers | Expected Number of Cancers* | SIR† (obs/exp) | 95% CI | Observed Number of Cancers | Expected Number of Cancers* | SIR† (obs/exp) | 95% CI |
| Random twin 1 |
Random twin 2 |
||||||||
| Males | 0–49 y | 64 | 55.3 | 1.16 | 0.91–1.48 | 68 | 56.1 | 1.21 | 0.95–1.54 |
| 50–59 y | 38 | 34.1 | 1.11 | 0.81–1.53 | 38 | 37.6 | 1.01 | 0.74–1.39 | |
| 60–69 y | 106 | 91.6 | 1.16 | 0.96–1.40 | 102 | 92.4 | 1.10 | 0.91–1.34 | |
| 70–79 y | 198 | 216.1 | 0.92 | 0.80–1.05 | 150 | 166.0 | 0.90 | 0.77–1.06 | |
| 80–89 y | 149 | 173.4 | 0.86 | 0.73–1.01 | 169 | 189.8 | 0.89 | 0.77–1.04 | |
| 90+ y | 51 | 65.1 | 0.78 | 0.60–1.03 | 49 | 72.7 | 0.67 | 0.51–0.89 | |
| Total | 606 | 635.7 | 0.95 | 0.88–1.03 | 576 | 614.6 | 0.94 | 0.86–1.02 | |
| Females | 0–49 y | 59 | 57.0 | 1.04 | 0.80–1.34 | 55 | 60.8 | 0.90 | 0.69–1.18 |
| 50–59 y | 42 | 35.5 | 1.18 | 0.87–1.60 | 45 | 36.0 | 1.25 | 0.93–1.68 | |
| 60–69 y | 68 | 68.5 | 0.99 | 0.78–1.26 | 83 | 68.4 | 1.21 | 0.98–1.50 | |
| 70–79 y | 121 | 153.2 | 0.79 | 0.66–0.94 | 160 | 145.7 | 1.10 | 0.94–1.28 | |
| 80–89 y | 216 | 245.4 | 0.88 | 0.77–1.01 | 237 | 263.5 | 0.90 | 0.79–1.02 | |
| 90+ y | 125 | 154.5 | 0.81 | 0.68–0.96 | 131 | 142.7 | 0.92 | 0.77–1.09 | |
| Total | 631 | 714.1 | 0.88 | 0.82–0.96 | 711 | 717.0 | 0.99 | 0.92–1.07 | |
| Males + females | 0–49 y | 123 | 112.2 | 1.10 | 0.92–1.31 | 123 | 116.9 | 1.05 | 0.88–1.26 |
| 50–59 y | 80 | 69.6 | 1.15 | 0.92–1.43 | 83 | 73.5 | 1.13 | 0.91–1.40 | |
| 60–69 y | 174 | 160.2 | 1.09 | 0.94–1.26 | 185 | 160.8 | 1.15 | 1.00–1.33 | |
| 70–79 y | 319 | 369.3 | 0.86 | 0.77–0.96 | 310 | 311.7 | 0.99 | 0.89–1.11 | |
| 80–89 y | 365 | 418.8 | 0.87 | 0.79–0.97 | 406 | 453.3 | 0.90 | 0.81–0.99 | |
| 90+ y | 176 | 219.6 | 0.80 | 0.69–0.93 | 180 | 215.4 | 0.84 | 0.72–0.97 | |
| Total | 1,237 | 1,349.8 | 0.92 | 0.87–0.97 | 1,287 | 1,331.6 | 0.97 | 0.92–1.02 | |
Notes: CI = confidence interval; SIR = standardized incidence rate ratio. Test for trend in SIRs associated with age of cotwin at death resulted in a statistically significant decline in SIRs in all groups except for the random twin 2 women where the decline was less steep and only marginally statistically significant. The p values were .002, .031, .0001, .001, .103, and .001, respectively, for random twin 1 men, women, men + women, and random twin 2 men, women, and men + women.
Based on age-, sex-, and calendar time–specific cancer incidence in the general population.
Standardized incidence rate ratio.