Charles Wood, MD Updated By: Lara Bonner Millar, MD The Abramson
Cancer Center of the University of Pennsylvania Last Modified:
June 1, 2011 Thymoma is a rare tumor of the thymus gland, which
is a small organ that lies under the breastbone, in a part of
the body known as the "anterior mediastinum." The thymus is part
of the immune system and is responsible for the development of
lymphocytes, which are cells that travel through the body and
help to fight infection. As we age, the thymus regresses, but in
some people a remnant remains in adulthood. Thymoma is usually a
slow-growing tumor that does not typically spread beyond the
thymus gland. It is the most common tumor seen in the anterior
mediastinum in adults. Thymic carcinoma, on the other hand, is
less common but more aggressive. It is generally more difficult
to treat because it tends to spread quickly to other areas of
the body. The cause of thymoma is unknown, and the risk factors
have not been identified. It affects men and women equally, most
often in