Thymus Cancer: Introduction

What is cancer?

Cancer is when cells in the body change and grow out of control. Your body is made up of tiny building blocks called cells. Normal cells grow when your body needs them, and die when your body does not need them any longer.

Cancer is made up of abnormal cells that grow even though your body doesn't need them. In most cancers, the abnormal cells grow to form a lump or mass called a tumor. If cancer cells are in the body long enough, they can grow into (invade) nearby areas. They can even spread to other parts of the body (metastasis).

What is thymus cancer?

Thymus cancer is cancer that starts in the thymus. This is a small organ in the front part of your chest under the breastbone. When your body is forming and growing during pregnancy and childhood, the thymus makes a type of white blood cell called a T-lymphocyte. These blood cells are important to your immune system. They grow in the thymus and then travel to the lymph nodes. This is where they help protect your body against infections. 

The thymus is lined by epithelial cells on its outer surface. These cells are where thymus tumors start. 

Types of thymus tumors

There are 2 main types of thymus tumors. Both of them are rare.


These are the more common type of tumor in the thymus. Most thymomas are slow growing, but they can be cancerous. They can also spread to other parts of your body. There are different types of thymomas. When your healthcare provider finds a thymoma, it’s classified based on 2 factors. These include how the cells look under a microscope and whether it’s spread past the thymus (and, if so, how far). Thymomas often show up with an autoimmune disease, such as myasthenia gravis.

Thymic carcinomas

These tumors also form from epithelial cells in the thymus, but they grow more quickly. They have often spread to other parts of your body by the time they are found.

There are other types of tumors that can start in the thymus, but these are very rare. These include carcinoids of the thymus.

Talk with your healthcare provider

If you have questions about thymus cancer, talk with your healthcare provider. He or she can help you understand more about this cancer.

Online Medical Reviewer: Lu Cunningham
Online Medical Reviewer: Richard LoCicero MD
Date Last Reviewed: 4/1/2019
© 2021 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare provider's instructions.