S100B and pituitary tumor: S100B is expressed in non-endocrine cells of the pituitary, which are also described in pituitary neoplasms, suggesting they might play a role in tumourigenesis-related processes.94–96 The expression of S100B protein was investigated in 54 PTs and in four normal pituitaries, and it is reported that decreased expression was observed in PTs compared with normal pituitaries.