Objectives: Since large cell neuroendocrine carcinoma (LCNEC) is a relatively rare histologic type of primary lung cancer, little is known about the immunological status of patients with LCNEC. We aimed to clarify the expression and prognostic impact of programmed cell death ligand 1 (PD-L1), CD8, CD4, and Forkhead box protein P3 (Foxp3) in LCNEC.
Methods: We retrospectively analyzed PD-L1, CD8, CD4, and Foxp3 expressions in 95 surgically resected LCNEC. PD-L1 positive staining was determined in tumors with more than 1% of tumor cells stained to any intensity, and CD8, CD4, and Foxp3 positivity was determined in tumors with more than 5% of lymphocytes stained.
Results: Positive expression of PD-L1, CD8, CD4, and Foxp3 was observed in 70 (74%), 52 (55%), 76 (80%), and 43 (45%) tumors, respectively. The expression of PD-L1 was significantly correlated with positive lymphatic permeation. Positive correlations were mutually observed among tumor infiltrating immune cells. Univariate and multivariate analyses showed that positive pleural invasion and Foxp3 negative expression were independent unfavorable prognostic factors for overall survival (OS). Advanced pathological stage, positive pleural invasion, CD4 negative expression in cancer stroma, and Foxp3 negative expression were identified as independent unfavorable prognostic factors for recurrence free survival (RFS).
Conclusions: Foxp3 positive tumor infiltrating lymphocytes (TILs) were an independent favorable prognostic factor for both OS and RFS, whereas CD4 positive TILs were an independent significant unfavorable prognostic factor for RFS. The high frequency of PD-L1 expression could support the use of anti-programmed cell death 1 antibody in the treatment of LCNEC.
Keywords: Foxp3; Large cell neuroendocrine carcinoma (LCNEC); PD-L1; lung cancer; tumor infiltrating lymphocyte (TIL).