Background: Pituitary adenomas (PAs) are the second most common brain tumors, and mostly are benign tumors. However, there exists subtypes of PAs refractory to common treatments, and need novel therapy. Programmed death 1 (PD-1) blockade has shown durable objective response in a variety of malignancies, and the key predictive markers for this immunotherapy were PD-L1 and CD8+ tumor-infiltrating lymphocyte (TILs) expression. To evaluate the potential immunotherapy for PAs, we investigated the expression of these two immune markers in PAs.
Methods: Immunohistochemistry (IHC) was performed to detect the expression of PD-L1 and CD8+ TILs in PAs. The ratio of positive expression of PD-L1 and CD8+ TILs was compared with chi-squared tests among different subtypes of PAs. The association between their expression profile and clinical parameters was analyzed using a chi-squared test, or Fisher's exact probability test when appropriate.
Results: One hundred and ninety one patients with PAs were retrospectively involved in this study, consisting of 106 non-functioning PAs (NF-PAs, 55.5%), 40 PRL-secreting PAs (PRL-PAs, 20.9%), 31 GH-secreting PAs (GH-PAs, 16.2%), 9 ACTH-secreting PAs (ACTH-PAs, 4.7%) and 5 plurihormonal adenomas (2.6%) respectively. 36.6% of them were PD-L1 positive and 86.9% were CD8+ TILs positive. The positive PD-L1 immunostaining presented more frequently in functioning PAs (58.8%), compared with that (34.3%) in nonfunctioning group (p = 0.000). Moreover, the rates of PD-L1 expression were more associated with increased blood levels of PRL, GH, ACTH and cortisol. Contrastly, positive CD8+ TILs immunostaining was only correlated with elevated blood level of GH. For the analysis of immune markers with pathological results, PD-L1 expression was associated with PRL and GH immunostaining and higher Ki-67 index. But CD8+ TILs was only correlated with PRL immunostaining.
Conclusion: Our results showed that PD-L1 was frequently expressed in functioning PAs with association of aggressive behaviors in PAs. The immunotherapy could be a promising treatment option of PAs.
Keywords: CD8+ lymphocyte; Immunotherapy; PD-L1; Pituitary adenomas.