Objective To investigate the expression of microRNA-451 (miR-451) and toll-like receptor 4 (TLR4) in peripheral blood of lung cancer patients complicated with pulmonary infection (PI) and their clinical significance.

Methods A total of 60 lung cancer patients complicated with PI were retrospectively selected and were included in PI group. Based on the pneumonia severity index (PSI) score, they were further divided into mild group (14 cases), moderate group (28 cases) and severe group (18 cases). Additionally, 60 patients with lung cancer without PI during the same period were selected as non-PI group. The expression levels of miR-451 and TLR4 mRNA in peripheral blood were compared between the PI and non-PI groups. Multivariate Logistic regression analysis was used to screen for influencing factors. A receiver operating characteristic (ROC) curve was plotted, and the area under the curve (AUC) was used to evaluate the diagnostic efficacy. The expression levels of miR-451 and TLR4 mRNA in peripheral blood of lung cancer patients complicated with PI of different severities were compared. Pearson correlation analysis was employed to explore the correlation between their expression levels and the severity of lung cancer complicated with PI.

Results Compared with the non-PI group, the expression level of miR-451 in peripheral blood of patients in the PI group was decreased, while the expression level of TLR4 mRNA was increased (P < 0.05). Multivariate Logistic regression analysis revealed that the expression levels of miR-451 and TLR4 in peripheral blood were both influencing factors for lung cancer patients complicated with PI (P < 0.05). ROC curve analysis showed that the AUC values for the diagnosis of lung cancer complicated with PI using miR-451, TLR4 alone, and their combination were 0.805, 0.779 and 0.888, respectively. In the mild, moderate, and severe groups, the expression level of miR-451 in peripheral blood decreased in sequence, while the expression level of TLR4 mRNA increased in sequence (P < 0.05). Pearson correlation analysis indicated that the expression level of miR-451 in peripheral blood was negatively correlated with the PSI score and the expression level of TLR4 (r=-0.697, -0.579, P < 0.001), while the expression level of TLR4 in peripheral blood was positively correlated with the PSI score (r=0.751, P < 0.001).

Conclusion Both miR-451 and TLR4 are abnormally expressed in the peripheral blood of lung cancer patients complicated with PI, and their expression levels are closely related to the severity of PI. The combined detection of the two has a high diagnostic value for lung cancer complicated with PI.