TMIC-02. SINGLE-CELL HIGH-DIMENSIONAL MASS CYTOMETRY (CYTOF) REVEALS IMMUNE LANDSCAPE OF PITUITARY NEUROENDOCRINE TUMORS

Abstract Pituitary neuroendocrine tumors (pitNETs) are a group of neoplasms in the sellar region, ranking as the second most common primary brain tumors, with some exhibiting aggressive behaviors. While immunohistochemical staining has been utilized to characterize the tumor immune microenvironment (TIME) of pitNETs, single-cell analysis remains underexplored. High-dimensional mass cytometry (CyTOF) offers a valuable approach for precise quantification of intratumoral leukocytes and potential therapeutic insights. We prospectively enrolled 56 patients with pitNETs of varying endocrine function, histology, and lineage. CyTOF, employing heavy metal-tagged antibodies, was employed to simultaneously measure 37 cellular parameters at single-cell resolution. Analysis revealed a total of 71,049 CD45+ immune cells. Macrophages (mean, 50.7%) and T cells (mean, 28.7%) were the predominant leukocytes, followed by NK cells, dendritic cells, B cells, and neutrophils. The immune cell composition within the TIME exhibited heterogeneity, with distinct patterns observed between functioning and non-functioning pitNETs. Functioning pitNETs displayed fewer macrophages (28.9% vs. 62.9%) and more T cells (44.9% vs. 19.6%) compared to non-functioning pitNETs. Subgroups within functioning (somatotroph, mammosomatotroph, lactotroph) and those within non-functioning pitNETs (null-cell, gonadotroph, corticotroph) shared similar immune profiles, respectively. PIT-1 lineage pitNETs demonstrated a T cell-dominated pattern, while SF-1, T-PIT, and null-cell lineage pitNETs exhibited macrophage predominance. In functioning pitNETs, macrophage abundance negatively correlated with invasiveness, Ki-67 index, and recurrence, while CD4 T cells showed positive correlations. Further unsupervised clustering identified 27 subpopulations of intratumoral immune cells, with some serving as critical predictors of tumor behavior. Our study provides a comprehensive single-cell immune profile of pitNETs, revealing distinct features across subtypes and targeted therapeutic implications.