Table 3.
Summary relative risk (RR) estimates [95 % confidence intervals (CIs)] for case–control and cohort studies of the association between insulin treatment and cancer incidence and mortality by study design, geographical area, and duration of follow-up
| Subgroup | Number of studies | Summary RR (95 % CI) | Between studies | Between subgroups | ||
|---|---|---|---|---|---|---|
| I 2 | P heterogeneity | Q | P heterogeneity | |||
| Study design | ||||||
| Case–control | 5 | 1.83 (0.99, 3.38) | 74.7 % | 0.003 | 3.80 | 0.051a |
| Cohort studies | 10 | 1.28 (1.03, 1.59) | 88.1 % | 0.001 | ||
| Geographical area | ||||||
| USA | 5 | 1.90 (1.17, 3.09) | 84.9 % | 0.001 | 45.20 | 0.001b |
| Europe | 9 | 1.34 (1.14, 1.57) | 65.7 % | 0.003 | ||
| Asia | 1 | 0.17 (0.09, 0.32) | – | – | ||
| Type of DM | ||||||
| Type 2 | 8 | 1.30 (0.89, 1.90) | 89.0 % | 0.001 | 6.64 | 0.010c |
| Type 1 and 2 | 7 | 1.44 (1.12, 1.85) | 75.9 % | 0.001 | ||
| Follow-up duration | ||||||
| ≤4 years | 5 | 1.02 (0.77, 1.35) | 91.7 % | 0.001 | 7.47 | 0.006d |
| >4 years | 5 | 1.82 (1.20, 2.76) | 79.5 % | 0.001 | ||
All statistical tests were two-sided
aTest for heterogeneity between case–control and cohort studies
bTest for heterogeneity between USA and combined Europe and Asia
cTest for heterogeneity between combined type 1 and 2 and type 2 diabetes
dTest for heterogeneity between follow-up duration ≤4 and >4 years