Cushing's Syndrome is caused by a tumor on which gland?

Cushing's Syndrome is primarily caused by an abnormality in the pituitary gland, which results in excessive production of adrenocorticotropic hormone (ACTH). This hormone stimulates the adrenal glands to produce cortisol, leading to the various symptoms associated with Cushing's, such as weight gain, changes in skin appearance, and increased vulnerability to infections.

In most cases of Cushing's Syndrome, the underlying issue is a tumor located in the pituitary gland, which can lead to overproduction of ACTH. While tumors can also occur in the adrenal glands, causing primary hypercortisolism, the classic cause commonly referenced for Cushing's Syndrome is indeed the pituitary tumor, often referred to as Cushing's disease when specifically caused by this pituitary issue.

The other options are associated with different endocrine disorders or conditions but do not lead to the classic presentation of Cushing's Syndrome. Understanding the specific function of the pituitary gland and its regulatory effect on the adrenal glands is crucial for recognizing how Cushing's Syndrome develops.