The pituitary gland, a small, pea-sized structure at the base of the brain, is central to the endocrine system. It functions as the “master gland,” orchestrating hormone production and release for growth, metabolism, reproduction, and stress responses. Abnormal growths can sometimes develop within its tissues. This article explores the nature of these growths and how frequently they are cancerous.
What Are Pituitary Tumors?
Pituitary tumors are abnormal cell growths within the pituitary gland. These growths can disrupt the gland’s normal function by either producing excess hormones or by pressing on surrounding structures. Most pituitary tumors are categorized as adenomas, which are non-cancerous growths from glandular tissue.
These adenomas are classified into two main types based on their hormonal activity. Functional adenomas produce and secrete excess hormones. Non-functional adenomas do not secrete hormones, impacting primarily due to their size and pressure on adjacent areas. Tumors are also classified by size, with microadenomas being less than 10 millimeters and macroadenomas being 10 millimeters or larger.
The Malignancy Question: How Often Are They Cancerous?
Pituitary tumors are mostly non-cancerous. Malignant pituitary tumors, known as pituitary carcinomas, are rare. They account for less than 0.2% of all pituitary tumors diagnosed, meaning over 99.8% do not spread.
This low incidence of malignancy means that most individuals diagnosed with a pituitary tumor will not have cancer. The primary concern with the vast majority of pituitary tumors is their potential to disrupt hormone levels or press on nearby brain structures.
Understanding Benign Pituitary Tumors
While not cancerous, benign pituitary tumors can impact health. Functional adenomas can produce excess hormones. For example, excess prolactin can cause irregular menstrual cycles in women, erectile dysfunction in men, and milk discharge from the breasts.
An excess of growth hormone can cause acromegaly in adults, causing enlarged hands, feet, and facial features, or gigantism if it occurs during childhood. Adrenocorticotropic hormone (ACTH) secreting tumors can result in Cushing’s disease, leading to weight gain, skin thinning, muscle weakness, and high blood pressure. These imbalances require medical management to alleviate symptoms and prevent complications.
Mass effect is another impact of benign pituitary tumors, especially macroadenomas. As these tumors grow, they can press on surrounding brain structures. This compression can affect the optic nerves, located above the pituitary gland, leading to vision problems such as loss of peripheral vision or even blindness if left untreated.
They can also press on the normal pituitary tissue itself, impairing the gland’s ability to produce necessary hormones. This can result in hypopituitarism, requiring hormone replacement therapy. Headaches are another common symptom associated with the mass effect of larger pituitary tumors.
When Pituitary Tumors Are Cancerous
A cancerous pituitary tumor is termed a pituitary carcinoma. A pituitary carcinoma is distinguished from a benign adenoma by its ability to metastasize, or spread. Spread can occur to the central nervous system (brain or spinal cord) or distant sites like bones, liver, or lungs.
Diagnosing a pituitary carcinoma primarily relies on evidence of this metastatic spread, as the primary tumor may appear histologically similar to a benign adenoma. Tumor cells in distant tissues confirm malignancy. Without metastasis evidence, even an aggressive-looking pituitary tumor is classified as an atypical adenoma.
These malignant tumors are more aggressive and challenging to treat than their benign counterparts. Treatment often involves surgery, radiation, and systemic chemotherapy. Despite the need for more aggressive interventions, these cancerous forms of pituitary tumors remain exceptionally rare.