PRLR and hyperprolactinemia: Regarding the CNS, there are studies showing the presence of hyperprolactinemia, intracellular PRL and PRL receptor (PRL-R) in different types of CNS tumors [12,13], and intracellular PRL and serum PRL were associated with a tendency of increased vascular density and significant increase of cell proliferation markers Ki-67 and Mcm-2, suggesting that PRL may play a role in the development of these tumors [14].