What is cancer?
Cancer is a group of diseases characterized by uncontrolled growth of abnormal cells. Most of the more than 200 types of cancer are named for the site where the abnormality was first discovered. For example, cancer that starts in basal cells of the skin is called basal cell carcinoma. And while cancer may spread or metastasize, it is still named according to its origin. For example, lung cancer that has spread to the liver is still called lung cancer.
Many cancers fall into one of these main types:
All cancers begin in the body’s cells. As cells become old or damaged, the body replaces them with new cells needed to maintain health. But sometimes this process gets derailed. Cells’ genetic material changes or becomes damaged, cells refuse to die, and unnecessary new cells are formed.
Explore this section to learn more about cancer, and search our cancer types  pages for detailed information about specific cancer diagnosis.