Background: Small cell lung cancer and non-small cell lung cancer are the two main types of lung cancer and major causes of cancer-related death worldwide.
Objectives: To compare serum cytotoxic T-lymphocyte-associated antigen 4 levels between treated and untreated patients with small cell lung cancer and non-small cell lung cancer, and healthy controls.
Methods: This case-control study was conducted at the Oncology Teaching Hospital, Baghdad, Iraq, from December 2024 to June 2025. The study included 180 participants: 24 patients with small cell lung cancer, 96 with non-small cell lung cancer, and 60 healthy controls. Serum cytotoxic T-lymphocyte-associated antigen 4 levels were measured using enzyme-linked immunosorbent assay, and complete blood count parameters were measured using an automated hematology analyzer.
Results: Cytotoxic T-lymphocyte-associated antigen 4 levels differed significantly among the control, small cell lung cancer, and non-small cell lung cancer groups (p = 0.02), with higher levels in small cell lung cancer and lower levels in non-small cell lung cancer than controls. No significant differences were observed between treated and untreated patients in either group. Cytotoxic T-lymphocyte-associated antigen 4 levels were significantly associated with Programmed death-ligand 1 categories in treated non-small cell lung cancer patients (p = 0.01), but not in untreated patients (p = 0.12). Complete blood count parameters differed significantly among the study groups, suggesting systemic inflammatory changes. Serum cytotoxic T-lymphocyte-associated antigen 4 showed limited diagnostic performance.
Conclusion: Cytotoxic T-lymphocyte-associated antigen 4 levels were significantly associated with Programmed death-ligand 1 expression in treated patients. Complete blood count, cytotoxic T-lymphocyte-associated antigen 4, and Programmed death-ligand 1 may provide useful information on the inflammatory and immunological status of lung cancer patients, but further studies are needed to confirm their clinical significance.