Lower serum levels of bilirubin in the newly diagnosed lung cancer patients: A case-control study in China

Purpose: A few prospective studies demonstrated that bilirubin levels were inversely associated with the risk of lung cancer. However, the retrospective study about the relationship between bilirubin levels and lung cancer in China was not available. So, we want to know whether there has a difference in serum bilirubin concentrations between normal people and lung cancer patients. Materials and Methods: Using a case-control study, we investigated the bilirubin levels in 317 patients with lung cancer and 317 age-, sex-matched controls from Zhejiang Cancer Hospital. Furthermore, we analyzed the associations between serum bilirubin expressions and baseline clinical features of lung cancer patients using a Wilcoxon rank sum test. Results: Bilirubin levels, including total bilirubin, direct bilirubin, and indirect bilirubin, were significantly lower in human lung cancer serum relative to normal control (P < 0.001), and the older (>50 years) had higher bilirubin levels compared with the younger (27-50 years) in lung cancer group. Besides, the duration of smoking was negatively related to bilirubin levels, but they did not reach statistical significance except for indirect bilirubin (P = 0.041). However, there was no difference in bilirubin levels between small cell lung cancer (SCLC) and non-SCLC (NSCLC), and we did not find that the bilirubin levels were correlated with sex, drinking status in patients of lung cancer. Conclusion: Serum total bilirubin, indirect bilirubin, and direct bilirubin levels of the patients with lung cancer were all significantly lower than those of control group (P < 0.001). Lower levels of bilirubin may be a risk factor for lung cancer, and it could serve as a potential screening biomarker for lung cancer. Large-scale investigations and additional improvements are urgently needed to demonstrate the mechanism and molecular pathway in order to achieve the clinical utility in the future.