Thymic Neoplasms and Myasthenia Gravis Overview

Thymic neoplasms are tumors that develop in the thymus gland.
People with thymic neoplasms frequently have myasthenia gravis — a chronic, progressive autoimmune disorder that causes the muscles of the head, face, and body to become weak and easily fatigued.

About the thymus gland and thymic neoplasms

The thymus gland sits in the upper chest area just behind the breastbone (sternum). Its purpose is to make white blood cells (lymphocytes) that protect against infection.
Different types of tumors can develop in the thymus. Doctors refer to these as thymic neoplasms.
Types of thymic neoplasms:

• Thymoma — the most common tumor of the thymus involving the cells on the outside surface of the thymus gland. Thymomas grow slowly and rarely spread (metastasize) to other parts of the body. The tumor cells in thymomas have a similar appearance to normal thymus gland cells. Thymomas are easier to treat than thymic carcinomas.
• Thymic carcinoma — a rare type of thymic gland cancer with cells that look radically different from normal thymus gland cells. This type of thymic neoplasm grows more rapidly and frequently spreads to other parts of the body by the time a doctor discovers the cancer. Thymic carcinomas are more difficult to treat than thymomas.

People with thymic neoplasms frequently have an autoimmune disease — such as myasthenia gravis — that causes the body’s immune system to attack healthy tissues and organs.
Learn more about thymic neoplasms at UPMC CancerCenter.

About myasthenia gravis

Myasthenia gravis is a chronic and progressive autoimmune disease in which the cranial, facial, and body muscles become very weak and easily fatigued. It can occur in people of any age, but commonly occurs in women under 40 and men over 60.

Causes of myasthenia gravis

Myasthenia gravis is an autoimmune disorder that causes your body’s immune system to attack healthy organs and tissues in your body, resulting in their destruction.
Normally, your nerves send your muscles messages through a receptor. Nerves use a chemical called acetylcholine to deliver these messages. When the acetylcholine binds to the receptor area of a nerve, the muscle contracts.
With myasthenia gravis, the immune system attacks the muscle's receptor for acetylcholine.
Experts don’t understand exactly why the body begins to produce immune antibodies that attack the acetylcholine receptors. However, it seems to relate in some way to the thymus gland, which assists the body in producing antibodies.
Approximately 15 percent of those with myasthenia gravis also have a thymoma.