Lymphocyte CD4/CD8 ratio predicts early immune-related toxicity in lung cancer patients treated with immune checkpoint inhibitors: a single-center retrospective study.

Background: We determined whether the baseline peripheral blood CD4/CD8 ratio predicts grade ≥2 immune-related adverse events (irAEs) within 30 days of initiating single-agent PD-1/PD-L1 blockade in advanced lung cancer. Method: In this single-center retrospective study (January 2022-December 2025), we included adults with pathologically confirmed advanced NSCLC who received first-line treatment with pembrolizumab, tislelizumab, sintilimab, and camrelizumab. Baseline flow cytometry performed within 7 days before cycle 1 was required. The primary endpoint was grade ≥2 irAEs within 30 days. Multivariate logistic regression was used to identify independent predictors and evaluate model performance (area under the curve [AUC]). Results: Among 202 patients, 51 (25%) developed grade ≥2 irAEs. Median onset ranged from 2.1 weeks (rash) to 3.0 weeks (endocrine). Baseline CD4/CD8 ratio < 1.65 remained was present in 63% of patients with early irAE vs. 36% of controls ( Conclusion: A pre-treatment CD4/CD8 ratio <1.65 remained is a simple, inexpensive biomarker that identifies lung cancer patients at high risk for early irAEs during single-agent PD-1/PD-L1 blockade. Prospective, multicenter validation is warranted.