One possible reason for these interesting results is that in the no prolactinoma subgroup, the positive correlation between the Ki-67 index and prolactin is due to “stalk effect.” Higher Ki-67 tends to show up in larger PAs and leads to a more severe “stalk effect.” Because dopamine inhibits the basally high-secretory tone of lactotrophs, when the tumor mass blocks the infundibular dopamine release, hyperprolactinemia will occur (48). Here, MKI67 is linked to hyperprolactinemia.