Peripheral and tissue immune biomarkers in pituitary neuroendocrine tumors: preliminary results from the MAESTRO study

Introduction: Increasing evidence indicates that immune and angiogenic components of the tumour microenvironment (TME) contribute to the biological behaviour of pituitary neuroendocrine tumours (PitNETs). However, the relationship between systemic immune composition and local tumour immune architecture remains poorly characterized. Aim of the study: This exploratory study aimed to investigate immune heterogeneity in PitNETs by integrating peripheral immune profiling with TME assessment across clinical subtypes. Materials and Methods: Eighty-eight patients with a clinical or radiological diagnosis of pituitary lesions were screened. Inclusion criteria were ages 20-85 years; both sexes; clinical or radiological diagnoses of PitNET; histopathological diagnosis of PitNETs. Blood samples were analysed to evaluate Peripheral Blood Mononuclear Cells (monocytes, natural killer, and lymphocytes), and immunohistochemical staining on pituitary tissue was performed to characterize the TME. Results: 49 subjects were enrolled. Tumour size and invasiveness differed across clinical subtypes, with non-functioning tumours presenting larger and more frequently invasive lesions. Peripheral immune composition varied according to phenotype: patients with Cushing’s disease (CD) exhibited higher circulating CD8⁺ T lymphocytes (49.07 ± 24.96; NFPT 33.65 ± 12.03; ACRO 26.16 ± 11.63, p = 0.0061) and lower classical CD14⁺⁺CD16⁻ monocytes compared with ACRO and NFPT (CD 79.15 ± 13.45; ACRO 90.65 ± 5.34; NFPT 89.67 ± 4.46; respectively, p = 0.002). TME analysis revealed reduced CD3⁺ T-cell infiltration in CD (1.18 ± 0.98 vs ACRO 4.56 ± 2.39, respectively; p = 0.003), while macrophage markers showed no significant subtype-specific differences. An inverse correlation was identified between the peripheral blood percentage of CD19⁺ B lymphocytes and CD34⁺ extravascular expression in TME (p = 0.047, r = 0.418), and between the tumourinfiltrating number of CD3⁺ T lymphocytes and the peripheral blood percentage of non-classical CD14⁺CD16⁺⁺ monocytes (p = 0.034, r = 0.443); while a positive correlation was detected between the tumour-infiltrating number of CD3⁺ T lymphocytes and the peripheral blood percentage of classical CD14⁺⁺CD16⁻ monocytes (p = 0.004, r = 0.528). Conclusions: This exploratory study provides integrated evidence that peripheral and tumour-associated immune profiles vary across PitNET subtypes and relate to tumour burden. Peripheral immune alterations appear linked to TME features but do not fully reflect its complexity. These findings support further investigation of combined systemic and tissue-level immune profiling as a hypothesis-generating strategy for biomarker development and biological characterization of PitNETs.