Among those who smoked ≥40 pack-years, those carrying IGF1 (CA)19/(CA)19 and (CA)19/X genotypes (OR = 6.14, 95% CI = 3.10–12.15) and IGF1 X/X genotype (OR = 5.43, 95% CI = 2.84–10.36) also had significantly increased risk of lung cancer. Here, IGF1 is linked to lung cancer.