IGF1 and prostate cancer: Grouped by study design type, the combined OR of nested case-control studies within cohort (NCC, 10 studies) was 1.15 (95% CI: 1.00–1.32, P = 0.0443), indicating a statistically significant association between high IGF-I levels and increased risk of prostate cancer, and the heterogeneity was at a moderate level (I2=54.5%); while other types of studies (including case-control, Mendelian randomization, etc., 6 studies) had a combined OR of 1.07 (95% CI: 0.98–1.18, P = 0.1143), with no statistical significance, and heterogeneity was also at a moderate level (I2=52.6%).