Question: How often are pituitary tumors not hormone secreting? Also, how often do non-functional pituitary tumors become functional for hormone secretion?   

Answer: The incidence of non-functioning tumors depends on what is being reported. For example, whether the numbers are obtained from those requiring surgery, observed on an MRI or CAT scan, or from population based studies. Roughly 60-70% of the pituitary tumors I see in my practice are non-functional. It has been reported that approximately 10% of the population could have a non-functional pituitary tumor. If a tumor is shown to be non-functional by biochemical testing, it is decidedly uncommon for it to become hormone secreting. That said, patients with non-functional pituitary tumors should periodically have a pituitary MRI to ensure detection of any tumor growth.

By Dr. Nelson Oyesiku, Neurosurgeon, Spring, 2015