Thymoma and thymic carcinoma are diseases in which malignant (cancer) cells form on the outside surface of the thymus.

The thymus, a small organ that lies in the upper chest under the breastbone, is part of the lymph system. It makes white blood cells, called lymphocytes, that protect the body against infections.

There are different types of tumors of the thymus. Thymomas and thymic carcinomas are rare tumors of the cells that are on the outside surface of the thymus. The tumor cells in a thymoma look similar to the normal cells of the thymus, grow slowly, and rarely spread beyond the thymus. On the other hand, the tumor cells in a thymic carcinoma look very different from the normal cells of the thymus, grow more quickly, and have usually spread to other parts of the body when the cancer is found. Thymic carcinoma is more difficult to treat than thymoma.


Having a disease called myasthenia gravis can affect the risk of developing thymoma.

People with thymoma often have other diseases as well. These diseases may include myasthenia gravis, polymyositis, lupus erythematosus, rheumatoid arthritis, thyroiditis, Sjögren syndrome, and hypogammaglobulinemia.


Possible signs of thymoma and thymic carcinoma include a cough and chest pain.

Sometimes thymoma and thymic carcinoma do not cause symptoms. The cancer may be found during a routine chest x-ray. The following symptoms may be caused by thymoma, thymic carcinoma, or other conditions. A doctor should be consulted if any of the following problems occur:

• A cough that doesn't go away.
• Chest pain.
• Trouble breathing.

Tests that examine the thymus are used to detect (find) thymoma or thymic carcinoma.

The following tests and procedures may be used:

• Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.

• Chest x-ray: An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.

• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, such as the chest, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.

• MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the chest. This procedure is also called nuclear magnetic resonance imaging (NMRI).

Thymoma and thymic carcinoma are usually diagnosed, staged, and treated during surgery.

A biopsy of the tumor is done to diagnose the disease. The biopsy may be done before or during surgery, using a thin needle to remove a sample of cells. This is called a fine-needle aspiration (FNA) biopsy. A pathologist will view the sample under a microscope to check for cancer. If thymoma or thymic carcinoma is diagnosed, the pathologist will determine the type of cancer cell in the tumor. There may be more than one type of cancer cell in a thymoma. The surgeon will decide if all or part of the tumor can be removed by surgery. In some cases, lymph nodes and other tissues may be removed as well.


Tests done to detect thymoma or thymic carcinoma are also used to stage the disease.

Staging is the process used to find out if cancer has spread from the thymus to other parts of the body. The findings made during surgery and the results of tests and procedures are used to determine the stage of the disease. It is important to know the stage in order to plan treatment.


There are three ways that cancer spreads in the body.

The three ways that cancer spreads in the body are:

• Through tissue. Cancer invades the surrounding normal tissue.
• Through the lymph system. Cancer invades the lymph system and travels through the lymph vessels to other places in the body.
• Through the blood. Cancer invades the veins and capillaries and travels through the blood to other places in the body.

When cancer cells break away from the primary (original) tumor and travel through the lymph or blood to other places in the body, another (secondary) tumor may form. This process is called metastasis. The secondary (metastatic) tumor is the same type of cancer as the primary tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer.


The following stages are used for thymoma:

Noninvasive thymoma (stage I)

In stage I, cancer is found only within the thymus. All cancer cells are inside the capsule (sac) that surrounds the thymus.


Invasive thymoma (stage II, stage III, and stage IV)

Invasive thymoma includes stage II, stage III, and stage IV.

• In stage II, cancer has spread through the capsule and into the fat around the thymus or into the lining of the chest cavity.

• In stage III, cancer has spread to nearby organs in the chest, including the lung, the sac around the heart, or large blood vessels that carry blood to the heart.

• Stage IV is divided into stage IVA and stage IVB, depending on where the cancer has spread.
  • In stage IVA, cancer has spread widely around the lungs and heart.
  • In stage IVB, cancer has spread to the blood or lymph system.

Thymic carcinomas have usually spread to other parts of the body when diagnosed.

The staging system used for thymomas is sometimes used for thymic carcinomas.


Recurrent Thymoma and Thymic Carcinoma

Recurrent thymoma and thymic carcinoma is cancer that has recurred (come back) after it has been treated. The cancer may come back in the thymus or in other parts of the body. Thymic carcinomas commonly recur. Thymomas may recur after a long time. There is also an increased risk of having another type of cancer after having a thymoma. For these reasons, lifelong follow-up is needed.