Serum iron status and the risk of lung cancer: a two-sample Mendelian-randomization study.

Background: Previous epidemiological studies have reported controversial findings about the potential causal association between iron status and lung cancer. This study sought to assess the potential causality of serum iron status and lung cancer using the Mendelian-randomization (MR) method. Methods: We selected the genetic variables for iron status from the Genetics of Iron Status (GIS) consortium comprising 48,972 samples from European populations. The following two analysis strategies for instrumental variables (IVs) were applied: a conservative approach (instruments related to four iron status markers), and a liberal approach (instruments related to each iron status marker). The summary-level data for lung cancer were obtained from the International Lung Cancer Consortium comprising 27,209 individuals from European populations. The causality between serum iron status and lung cancer was examined. Results: Using the conservative approach, a higher serum iron status was found to be causally correlated with lower risks of lung squamous cell carcinoma. The odds ratios of lung squamous cell carcinoma per standard deviation (SD) unit increment in the four iron status markers were 0.73 [95% confidence interval (CI): 0.60-0.89; P=0.002] in serum iron, 0.50 (95% CI: 0.33-0.77; P=0.002) in ferritin, 1.35 (95% CI: 1.09-1.67; P=0.006) in transferrin, and 0.80 (95% CI: 0.69-0.92; P=0.001) in transferrin saturation based on the inverse variance-weighted method. Similar results were found using the liberal approach. Conclusions: Genetically, a high serum iron status was inversely associated with the risk of lung squamous cell carcinoma. More research needs to be conducted to explore the underlying mechanisms and to determine the potential application value about preventing the occurrence of cancer.