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What is primary and secondary cancer?

The primary cancer is where the cancer started. If some of the cancer cells break away from the primary cancer and settle in another part of the body this cancer is then called a secondary cancer. Secondary cancers are made up of the same type of cells as the primary cancer. So, if you have breast cancer that has spread to the liver, you have primary breast cancer with secondary breast cancer in the liver.

This is important because doctors choose treatment according to the type of primary cancer. The cancer cells in the liver (in the example above) are actually breast cancer cells, not liver cells (see how breast cancer cells spread). So the treatment needs to be for breast cancer and not for primary liver cancer. 

There is more about what cancer is and about how cancer spreads in our about cancer section.

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Updated: 17 April 2013