ON THIS PAGE: You will find some basic information about these diseases and the parts of the body they may affect. This is the first page of Cancer.Net’s Guide to Thymoma and Thymic Carcinoma. Use the menu to see other pages. Think of that menu as a roadmap to this entire guide.
Thymoma and thymic carcinoma are types of cancer that begin in the thymus. The thymus is located under the breastbone, also called the sternum. It is a small organ that is part of the body’s immune system.
About the lymphatic system
The thymus is part of the lymphatic system. The lymphatic system is made up of thin vessels that branch out to all parts of the body. These vessels carry lymph. Lymph is a colorless fluid that carries away waste and transports a type of white blood cell call lymphocytes. Lymphocytes fight germs throughout the body. There are two kinds of lymphocytes:
B-lymphocytes make antibodies to fight bacteria. They may also be called B cells.
T-lymphocytes destroy foreign cells and trigger the B cells to make antibodies. They are also called T cells.
Early in life, the thymus is involved in the development and maturation of white blood cells, in particular T-lymphocytes. T-lymphocytes eventually travel to lymph nodes and around the body. In adulthood, the thymus is quite small and often replaced by fat.
Several other structures are involved in the lymphatic system:
Lymph nodes, which are small, bean-shaped organs that filter the lymph fluid. They are found in clusters in the neck, underarms, abdomen, pelvis, and groin. When bacteria get into the lymph nodes, they swell.
The spleen, which makes lymphocytes and filters blood
The tonsils, located in the throat
About thymoma and thymic carcinoma
Cancer begins when healthy cells change and grow out of control, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
There are different types of cancer that can start in the thymus. The thymus contains 2 main types of cells:
Epithelial cells. The cells that line the thymus are called thymic epithelial cells. When these cells change and grow out of control, it is considered thymoma or thymic carcinoma.
Thymomas are generally slow-growing tumors. Occasionally, it can spread to the lining of the lung, called the pleura. Less often, it can spread to other parts of the body. Thymic carcinoma (see Stages) also starts in the thymus. It is more likely to spread to the lining of the lungs and other parts of the body. Thymic carcinoma can also be more difficult to treat.
Rarely, another type of tumor called a thymic neuroendocrine tumor (TNET, previous called a carcinoid tumor) can develop in the thymus. TNETs can be difficult to treat and treatment depends on the type of TNET (see Stages). You can learn more about neuroendocrine tumors in another section of this website.
About 30% to 50% of people with thymic tumors also have a condition called myasthenia gravis. Myasthenia gravis is an autoimmune disorder caused by antibodies or T-cells that attack molecules, cells, or tissues of the person producing them. The main symptom of myasthenia gravis is fluctuating weakness in various muscles. It may affect any muscle that is under voluntary control, such as those that control eye movements, chewing, swallowing, coughing, and facial expression. Muscles that control breathing and movements of the arms and legs may also be affected in more severe cases. Myasthenia gravis may appear before a thymic tumor is diagnosed or it may develop during or after treatment.
In addition to myasthenia gravis, people with a thymic tumor may have other groups of syndromes, called paraneoplastic syndromes. These may include severe low red blood cell count or anemia, called pure red cell aplasia, or low levels of antibodies known as immunoglobulins in the blood, called hypogammaglobulinemia.
The next section in this guide is Statistics. It helps explain how many people are diagnosed with thymoma and thymic carcinoma and general survival rates. Use the menu to choose a different section to read in this guide.