Pituitary tumors are surprisingly common. Depending on how you look for them, they show up in roughly 1 in 6 people. A major meta-analysis of autopsy and radiological studies found pituitary adenomas at a rate of 14.4% in autopsy series and 22.5% in imaging studies. The vast majority of these are tiny, cause no symptoms, and go completely unnoticed throughout a person’s life. Clinically relevant pituitary tumors, the kind that actually produce symptoms and get diagnosed, are far less common, occurring in roughly 1 in 1,000 people.
Most Are Found by Accident
Pituitary incidentalomas, tumors discovered on brain imaging done for completely unrelated reasons like a headache workup or head injury, appear in 10% to 38% of adults and about 2% of children. These findings reflect how frequently small pituitary growths exist without ever causing trouble. Many are microadenomas, tumors smaller than 10 millimeters, that sit quietly in the pituitary gland and never grow large enough to press on surrounding structures or produce excess hormones.
The gap between how often these tumors exist and how often they cause problems is enormous. A cross-sectional study in Liège, Belgium found that verified, clinically relevant pituitary adenomas occurred at a prevalence of about 1 in 1,064 people. Even that number likely underestimates the true count, since the study wasn’t designed to catch tumors that were causing subtle hormonal changes without obvious symptoms. Still, the takeaway is clear: having a pituitary tumor is extremely common, but having one that matters to your health is much less so.
Types of Pituitary Tumors
Nearly all pituitary tumors are benign. The 2022 WHO classification officially renamed them from “pituitary adenomas” to pituitary neuroendocrine tumors (PitNETs), reflecting a better understanding of their biology. The name change hasn’t altered how common they are or how they’re treated in most cases, but it does acknowledge that these growths share characteristics with neuroendocrine tumors found elsewhere in the body.
The major types break down by what they do hormonally:
- Prolactinomas are the most common hormone-producing type. They release excess prolactin, which can cause irregular periods, unexpected breast milk production, and fertility problems. In women of childbearing age, smaller prolactinomas outnumber larger ones by a ratio of 20 to 1 compared to men.
- Non-functioning adenomas don’t produce excess hormones at all. They typically get noticed only when they grow large enough to press on the optic nerves (causing vision changes) or crowd out normal pituitary tissue. They occur at similar rates in men and women.
- Growth hormone-secreting tumors cause a condition called acromegaly, where the hands, feet, and facial features gradually enlarge. These also affect men and women at roughly equal rates and are most often diagnosed between ages 40 and 60.
- ACTH-secreting tumors cause Cushing disease, which leads to weight gain, easy bruising, and a distinctive rounding of the face. Women are affected about three times as often as men, and the condition disproportionately strikes younger women.
- TSH-secreting tumors (thyrotroph tumors) are the rarest type, making up as little as 0.07% of cases in large series.
Who Gets Diagnosed
Pituitary tumor diagnoses cluster in middle-aged and older adults, though the specific age range depends on the tumor type. Prolactinomas in women peak between ages 25 and 40, while growth hormone tumors tend to surface between 40 and 60. Among all patients diagnosed with a clinically evident pituitary adenoma, 62% to 77% are women. This skew is driven largely by prolactinomas and Cushing disease, both of which heavily favor women. Non-functioning adenomas and growth hormone tumors show no meaningful sex difference.
In children and adolescents, pituitary tumors are genuinely rare. A 46-year population-based analysis found an incidence of about 2.3 cases per 100,000 person-years in the pediatric age group. Among those, prolactinomas and non-functioning adenomas were the most common types, and overall rates have been trending upward over time, likely because of increased use of brain imaging rather than an actual rise in tumor formation.
Hereditary Connections
A small fraction of pituitary tumors are linked to inherited genetic syndromes. In people with a condition called MEN1 (multiple endocrine neoplasia type 1), pituitary tumors develop in 10% to 60% of cases, with prolactinomas being the dominant type. Another hereditary condition, Carney complex, leads to growth hormone-producing pituitary tumors in about 10% of affected individuals, though subtle hormonal abnormalities of the growth hormone system are much more common due to underlying changes in the gland’s tissue.
For the vast majority of people with a pituitary tumor, there is no identifiable genetic cause. These tumors arise spontaneously, and having one does not typically mean your family members are at elevated risk.
Malignant Pituitary Tumors Are Extremely Rare
True pituitary carcinomas, now reclassified as “metastatic PitNETs” under the 2022 WHO system, are vanishingly rare. A pituitary tumor is only classified as malignant if it spreads to distant sites in the body. This happens in a tiny fraction of cases. The overwhelming majority of pituitary tumors, even large or aggressive ones, remain benign and confined to the area around the pituitary gland. If you’ve been told you have a pituitary tumor, the odds that it’s cancerous are extremely low.
Why Detection Is Increasing
More pituitary tumors are being found now than in previous decades, but this almost certainly reflects better and more frequent imaging rather than a true increase in how often these tumors form. As MRI technology has improved and become more widely used, smaller and smaller lesions are being picked up incidentally. This creates a paradox: the more we scan, the more “abnormalities” we find, even though many of these findings require nothing more than periodic monitoring.
For most people with a small, incidentally discovered pituitary lesion, the clinical path forward involves checking hormone levels and possibly repeating imaging after several months to see if the tumor has grown. Many never require treatment at all.