NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,777 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

thymus
(THY-mus)
An organ that is part of the lymphatic system, in which T lymphocytes grow and multiply. The thymus is in the chest behind the breastbone.

EnlargeAnatomy of the thymus gland; drawing shows the thymus gland in the upper chest under the breastbone. Also shown are the ribs, lungs, and heart.

Anatomy of the thymus gland. The thymus gland is a small organ that lies in the upper chest under the breastbone. It makes white blood cells, called lymphocytes, which protect the body against infections.