Association of peripheral-blood neutrophil-to-lymphocyte ratio with Pneumocystis jirovecii pneumonia in patients with solid tumors: a case-control study

Background: The infection of Pneumocystis jirovecii pneumonia (PJP) increases the rate of malignancy-related death. It is crucial to estimate the risk of PJP in this population. Peripheral blood neutrophil-to-lymphocyte ratio (NLR) has been proven to have significant value in predicting bacterial infection. However, the associations between peripheral blood NLR and PJP in patients with solid tumors have not been investigated. We aimed to identify whether baseline peripheral-blood NLR was correlated with PJP in patients with solid tumors. Methods: We retrospectively reviewed medical records of all consecutive patients with solid tumors and a proven diagnosis of PJP according to the European Organization for Research and Treatment of Cancer (EORTC) consensus definitions. Patients were randomly grouped into a discovery cohort and a validation cohort in a 2:1 ratio. Propensity score matching was performed in a 1:2 ratio between patients with PJP and those without PJP. Demographic and clinical data were collected, which included malignancy types, baseline NLR, chest imaging, coexisting pulmonary disease, and treatment regimens. The receiver operating characteristic (ROC) curve was used to determine the optimal cutoff value of NLR for analyzing risk of PJP. Multivariate logistic analysis was performed to identify the risk factors of PJP. Results: A total of 249 patients were included, of whom 83 had PJP infection and 166 did not. A total of 157 (63.1%) patients were aged 65 years or older, 73.5% of participants were male, and 37.3% were never-smokers. Patients with PJP had a higher NLR level than those without PJP (P<0.001). The optimal threshold of NLR to predict PJP was 6.22. Multivariate analysis revealed independent associations with higher NLR (odds ratio: 4.96; 95% confidence interval: 1.82–13.50; P=0.002) and PJP after adjustment for age, sex, and smoking status. The incidence of PJP in the high-NLR subgroup (NLR ≥6.22) was significantly higher than that in the low-NLR subgroup (NLR <6.22) in the discovery (65.3% vs. 19.8%; P<0.001) and validation cohorts (65.4% vs. 19.0%; P<0.001). Moreover, NLR was negatively correlated with absolute CD4 and CD8 cell count. Patients with high NLR had a lower mean absolute CD4 and CD8 cell count than those with low NLR. Conclusions: Among patients with solid tumors, a baseline feature of high NLR (≥6.22) was independently associated with an increased risk of PJP development. Furthermore, the NLR demonstrates potential utility in assessing immune status. Therefore, clinicians should consider initiating PJP prophylaxis earlier or performing earlier PJP screening in patients with solid tumors and elevated peripheral blood NLR.