AbstractThe neural cell adhesion molecule (NCAM) has previously been studied in pituitary neuroendocrine tumours (PitNETs), but its role in tumour biology and aggressiveness remains controversial, and its relationship with the tumour microenvironment remains unknown. We aimed to characterise NCAM expression in PitNETs, to correlate this with clinico‐pathological features, and to assess the role of various microenvironment components on NCAM expression. NCAM and immune cells were investigated by immunohistochemistry in 16 human non‐functioning‐PitNETs (NF‐PitNETs) and eight somatotrophinomas, including macrophages (CD68, CD163, HLA‐DR), cytotoxic (CD8) and T helper (CD4) lymphocytes, regulatory T cells (FOXP3), B cells (CD20), and neutrophils (neutrophil elastase). Five normal pituitaries were included for comparison. The cytokine secretome from these PitNETs and from PitNET‐derived tumour‐associated fibroblasts (TAFs) were assessed on culture supernatants using a multiplex immunoassay panel. There were no significant NCAM expression differences between PitNETs and normal pituitary, and no difference between types of pituitary tumours (NF‐PitNETs vs. somatotrophinomas). There was no association between NCAM expression and different clinico‐pathological features, including cavernous sinus invasion and Ki‐67, nor with serum hormone levels. NCAM immunoreactivity correlated negatively with PitNET‐derived CXCL10 (rho = −0.417; p = .042) and CX3CL1 (rho = −0.423; p = .040) levels. NCAM immunoreactivity was negatively correlated with TAF‐derived fibroblast growth factor (FGF)‐2 (rho = −0.632; p = .009), but not with other TAF‐derived cytokines. Within the PitNET cohort, there were no correlations between NCAM immunoreactivity and immune infiltrates or ratios, although, within NF‐PitNETs, NCAM expression was higher in tumours with more FOXP3+ cells. NCAM expression does not differ between PitNETs and normal pituitary, and does not appear to relate to tumour invasiveness or proliferation. However, our data suggest a possible role for cytokines in the modulation of NCAM expression in PitNETs, particularly CXCL10, CX3CL1 and FGF‐2, but not for immune cell infiltrates.