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:

Stage I

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

Stage II

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

Stage III

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

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.