Prolactin is a hormone that triggers the breasts to produce milk (lactation).
Prolactinoma is the most common type of pituitary tumor (adenoma). It makes up at least 30% of all pituitary adenomas. Almost all pituitary tumors are noncancerous (benign). Prolactinoma may occur as part of an inherited condition called multiple endocrine neoplasia type 1 (MEN 1)
Prolactinomas occur most commonly in people under age 40. They are about five times more common in women than in men, but are rare in children.
At least half of all prolactinomas are very small (less than 1 cm or 3/8 of an inch in diameter). These small tumors are more common in women. They stay small and never get larger.
Larger tumors are more common in men. They tend to occur at an older age. The tumor can grow to a large size before symptoms appear.
The tumor is often detected at an earlier stage in women than in men.
Medicines that treat low thyroid function (hypothyroidism) and mental illnesses can raise prolactin level. This can cause symptoms similar to prolactinoma or an actual prolactinoma.