NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,790 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.

carcinoma in situ
(KAR-sih-NOH-muh in SY-too)
A group of abnormal cells that remain in the place where they first formed. They have not spread. These abnormal cells may become cancer and spread into nearby normal tissue. Also called stage 0 disease.

EnlargeTwo-panel drawing showing layers of tissue, including the outer tissue layer, muscle layers, connective tissue, and inner tissue layer. The left panel shows carcinoma in situ (abnormal cells) in the inner tissue layer. The right panel shows cancer cells spreading from the inner tissue layer to the connective tissue and muscle layers.

Carcinoma in situ (CIS) is a group of abnormal cells that are found only in the place where they first formed in the body (see left panel). These abnormal cells may become cancer and spread to nearby normal tissue (see right panel).