Types of Thymus Cancer

April 11, 2026

This page was reviewed under our medical and editorial policy by Amanda Reyes, M.D., Medical Oncologist, City of Hope^® Cancer Center Duarte. 

Thymus cancer is the name for any type of malignant tumor that develops in the cells of the thymus gland. The thymus gland is a small organ found in the chest near the heart and behind the breastbone. Its main role is to help produce T cell lymphocytes, often referred to simply as T cells. T cells are an essential part of the body’s immune system. Thymus cancer may form in several different types of cells in the thymus, including:

• Thymic epithelial tumors (TETs), which form in the epithelial cells that make up the structure of the thymus gland
• Thymic neuroendocrine tumors (TNETS), which form in the neuroendocrine cells that serve as a “bridge” between the nervous system (“neuro-”) and hormone-producing system (“-endocrine”)

Although all kinds of thymus cancer are rare, the two most common types are thymoma and thymic carcinoma.

Thymoma

Thymoma is the term used to describe a rare kind of thymic epithelial tumor (TET). There are several different types of thymoma, classified by the World Health Organization according to the cell’s shape and lymphocyte density, as listed below.

Type A thymoma: Also called spindle cell type, this is very rare, generally slow growing and has a good prognosis. Its cells look fairly similar to normal cells, but may be oval or differently shaped than normal.

Type AB thymoma: This is similar to type A, but the tumor also includes T cell lymphocytes.

Type B1 thymoma: This has cells that look like healthy thymus cells but with more T cell lymphocytes than normal.

Type B2 thymoma: This also includes more T cell lymphocytes, as well as enlarged epithelial cells.

Type B3 thymoma: This includes few T cell lymphocyte cells and epithelial cells that look fairly normal.

Thymic Carcinoma

Thymic carcinoma is another rare kind of thymic epithelial tumor (TET) and is usually more aggressive than thymoma. Thymic carcinoma cells look very abnormal when viewed in a lab and, in many cases, thymic carcinoma has already started to spread to nearby tissue when it is first detected.

Thymic Neuroendocrine Tumors

Thymic neuroendocrine tumors (TNETs) are a very rare kind of neuroendocrine tumor (NET). TNETs affect the neuroendocrine cells, which are a type of cell that allows the nervous system to communicate with the body’s hormone-producing system. There are several different types of TNETs, including:

• Typical carcinoid tumors, which tend to be slow-growing
• Atypical carcinoid tumors, which are are slightly faster-growing and more likely to spread
• Large cell neuroendocrine carcinoma, which is a very aggressive, high-grade type of tumor that is likely to spread
• Small cell carcinoma, which is a faster-growing, very aggressive and high-grade tumor that is also likely to spread