Section Editor: Matthew Cecchini MD PhD FRCPC
May 23, 2026
The thymus is a small organ in the upper chest, behind the breastbone and in front of the heart. It is part of the immune system and is most active during childhood, when it helps the body’s immune cells develop. When tissue is removed from the thymus, a pathologist examines it under a microscope and describes what they see in your pathology report.
This page brings together our guides to tumors of the thymus. The articles are grouped by type to help you find the one that matches your diagnosis. Select any article below to learn more.
Thymoma
Thymoma is the most common tumor of the thymus. Most thymomas grow slowly, but because they can grow into nearby tissue and occasionally spread, they are treated as a type of cancer. Thymomas are divided into several types based on how the cells look under the microscope. The articles explain how each type is diagnosed and what your pathology report describes.
Thymoma is the most common tumor of the thymus. This article gives an overview of the diagnosis, including the different types and what your pathology report describes.
You may find this helpful if your report mentions a thymoma, or you have a thymoma along with myasthenia gravis or another autoimmune condition.
Type A thymoma is a type of thymoma made of spindle-shaped cells. It is usually slow-growing with a very good outlook. This article explains what this diagnosis means.
You may find this helpful if your report mentions a type A thymoma.
Type AB thymoma is a common type of thymoma that combines features of type A and type B thymoma. It usually has a very good outlook. This article explains what this diagnosis means.
You may find this helpful if your report mentions a type AB thymoma.
Type B1 thymoma is a type of thymoma that contains a large number of immune cells along with the tumor cells. This article explains what this diagnosis means and what your report describes.
You may find this helpful if your report mentions a type B1 thymoma.
Type B2 thymoma is a type of thymoma in which the tumor cells are easier to see among the immune cells. This article explains what this diagnosis means and what your report describes.
You may find this helpful if your report mentions a type B2 thymoma.
Type B3 thymoma is a type of thymoma made up mostly of tumor cells. It is more likely than other thymomas to grow into nearby tissue. This article explains what this diagnosis means.
You may find this helpful if your report mentions a type B3 thymoma.
Thymic carcinoma
Thymic carcinoma is a less common but faster-growing cancer of the thymus. It is more likely than a thymoma to grow into nearby structures and spread to other parts of the body. The article explains what this diagnosis means.
Thymic carcinoma is a fast-growing cancer of the thymus. This article explains how it is diagnosed and what the details in your pathology report mean.
You may find this helpful if your report mentions thymic carcinoma.
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