functional tumor

A functional tumor is an endocrine tumor that keeps doing the cells' original job — making hormone — but does it without any restraint. Imagine an employee who not only refuses to clock out but ignores every instruction to stop working; the hormone keeps flowing regardless of whether the body needs it.

The key word is autonomy. Normal endocrine cells obey feedback: when hormone levels are high enough, the off-signal tells them to pause. A functional tumor has lost that off-switch, so it secretes on its own schedule and at its own rate. The result is a hormone-excess syndrome whose features depend entirely on which hormone is being made — cortisol, aldosterone, insulin, growth hormone, prolactin, catecholamines, and many others each produce a distinctive picture.

Because they advertise themselves through symptoms, functional tumors are often caught while still small. Confirming one usually involves measuring the hormone and then showing that it fails to suppress when given a normal off-signal — proof of autonomy. Treatment is typically surgical removal, sometimes with drugs that block hormone production or action while the patient is prepared for surgery.