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Primary Cancer - The original site where cancer first arose. Cancer is classified according the primary location of a tumor (or the place where the cancer began). When cancer spreads (metastasizes) from the primary location to other areas of the body, the metastatic tumor contains cells that are like those in the primary tumor. Thus, even when cancer has spread to a new location, it is still named after the part of the body where it originally started. For example, if breast cancer spreads to the lungs, it is called metastatic breast cancer (not lung cancer).
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