Thymoma - Stages

Approved by the Cancer.Net Editorial Board, 05/2016

ON THIS PAGE: You will learn about how doctors describe a cancer’s growth or spread. This is called the stage. Classification is also important in describing thymoma. To see other pages, use the menu.

Staging is a way of describing where the cancer is located, if or where it has spread, and whether it is affecting other parts of the body. Doctors use diagnostic tests to find out the cancer's stage, so staging may not be complete until all the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis, which is the chance of recovery. There are different stage descriptions for different types of cancers.

The most commonly used staging system for thymoma is called the Masaoka system, and it classifies thymoma into the following stages:

  • Stage I: The cancer is located only in the thymus and the capsule that surrounds the thymus.

  • Stage II: The cancer has spread into fat surrounding the thymus or into the lining of the lung next to the tumor, called the mediastinal pleura.

  • Stage III: The cancer has spread to other organs near the thymus, such as the lung, blood vessels, and the sac around the heart, called the pericardium.

  • Stage IVA: The cancer has spread more extensively into the lining of the lung or the sac around the heart.

  • Stage IVB: The cancer has spread to organs further away from the thymus, or has spread through the vessels carrying blood or lymph.

Classification

In addition to stage, thymoma can be classified into different categories developed by the World Health Organization (WHO). These categories are based on what the tumor cells look like under a microscope:

  • Type A thymoma. This is also called spindle cell thymoma or medullary thymoma. The chance of recovery for people with type A thymoma is good. Nearly 100% of people with this type live at least 15 years after diagnosis.

  • Type AB thymoma. Also called mixed thymoma, type AB thymoma is similar to type A thymoma. However, type AB thymoma has lymphocytes in the tumor. The chance of recovery for people with type AB thymoma is also good. About 90% of people with this type live at least 15 years after diagnosis.

  • Type B1 thymoma. This is also known as lymphocyte-rich thymoma, lymphocytic thymoma, predominantly cortical thymoma, and organoid thymoma. This type of thymoma has many lymphocytes in the tumor, but the cells of the thymus appear healthy. The chance of recovery for people with type B1 thymoma is also good. About 90% of people with this type live at least 20 years after diagnosis.

  • Type B2 thymoma. Type B2 thymoma is also known as cortical thymoma and polygonal cell thymoma. This type of thymoma also has many lymphocytes, like type B1 thymoma. However, the thymus cells do not appear healthy. About 60% of people with this type live at least 20 years after diagnosis.

  • Type B3 thymoma. Type B3 thymoma is also known as epithelial thymoma, atypical thymoma, squamoid thymoma, and well-differentiated thymic carcinoma. This type of thymoma has few lymphocytes, and the thymus cells look abnormal. Approximately 40% of people with this type live at least 20 years after diagnosis.

  • Thymic carcinoma (Type C thymoma).  Thymic carcinoma is more aggressive. Thymic carcinoma cells do not look like healthy thymus cells but like cancers that start in other parts of the body. This type of tumor is often advanced when diagnosed. About 35% of people with thymic carcinoma live at least 5 years after diagnosis. Around 28% of people with thymic carcinoma live at least 10 years. Thymic carcinoma is sometimes classified into 2 categories:

    • Low grade. Low-grade thymic carcinoma is linked with a better chance of recovery. Low-grade thymic carcinoma includes basaloid, mucoepidermoid, and well-differentiated squamous cell types.

    • High grade. High-grade thymic carcinoma is more likely to grow and spread quickly. High-grade thymic carcinoma includes anaplastic/undifferentiated, clear cell, poorly differentiated squamous cell, sarcomatoid, and small cell/neuroendocrine types.

It is important to remember that statistics on how many people are diagnosed with this type of cancer are an estimate. The estimate comes from data based on people with this cancer in the United States each year. So, your own risk may be different. Doctors cannot say for sure how long anyone will live with thymoma. Learn more about understanding statistics.

Source: National Cancer Institute.

Information about the cancer’s stage and classification will help the doctor recommend a specific treatment plan. The next section in this guide is Treatment Options. Or, use the menu to choose another section to continue reading this guide.