Objective To investigate the changes of platelet-to-lymphocyte ratio (PLR) in patients with idiopathic pulmonary fibrosis (IPF) complicated by lung cancer, and to explore the adjunctive diagnostic value of PLR for identifying lung cancer in patients with IPF.Methods A retrospective analysis was performed in 530 patients with IPF treated at Nanjing Drum Tower Hospital from January 2016 to September 2022, including 361 patients with IPF alone and 169 patients with IPF complicated by lung cancer. PLR was calculated from routine blood tests. ROC curves were used to evaluate the discriminative performance of PLR and related markers for lung cancer in patients with IPF. Results PLR, carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), and cytokeratin 19 fragment (CYFRA 21-1) were significantly higher in patients with IPF complicated by lung cancer than in those with IPF alone. Multivariate logistic regression showed that PLR (OR=1.013, 95%CI 1.008–1.017), CEA (OR=1.067, 95%CI 1.030–1.106), and NSE (OR=1.046, 95%CI 1.018–1.074) were independently associated with lung cancer in IPF patients. Restricted cubic spline analysis demonstrated a linear dose-response relationship between PLR and lung cancer risk in IPF patients. The incidence of lung cancer increased across PLR tertiles (16.4% vs. 35.2% vs. 44.1%, P<0.01). ROC analysis showed that the AUC of PLR was 0.711 (95%CI 0.664–0.758, P<0.001), and the optimal cutoff, sensitivity, specificity, and Youden index were 115.80, 65.2%, 62.1%, and 0.273, respectively. The discriminative ability of PLR alone was moderate. The combined model including PLR, CEA, NSE, and CYFRA 21-1 yielded an AUC of 0.782 (95%CI 0.739–0.825, P<0.001). Conclusions PLR is elevated in IPF patients with lung cancer and is associated with the presence of lung cancer. However, PLR alone shows only moderate discriminative ability and should not be interpreted as a standalone diagnostic marker. The combination of PLR with CEA, NSE, and CYFRA 21-1 may improve adjunctive identification of lung cancer in patients with IPF.
