NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,812 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.

polycythemia vera
(PAH-lee-sy-THEE-mee-uh VAYR-uh)
A disease in which there are too many red blood cells in the bone marrow and blood, causing the blood to thicken. The number of white blood cells and platelets may also increase. The extra blood cells may collect in the spleen and cause it to become enlarged. They may also cause bleeding problems and make clots form in blood vessels.