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What Is a Primary Site?

Cancers are named for the part of the body in which they originate. The point of origin is called the primary site. Doctors must identify the primary site in order to prescribe the best course of treatment.

  1. Significance

    • When a doctor can identify a cancer's primary site, he can best determine a course of treatment, which varies according to the type of cancer. The treatment for breast cancer, for example, differs from the treatment for skin cancer. Identifying the primary site of the cancer also helps establish surgical options, in some cases allowing removal of the primary tumor and preventing the spread of the cancer.

    Metastasized Cancer

    • Cancer spreads throughout the body from the primary site. This process is called metastasis. Cancer typically spreads through the lymphatic system. When a cancer spreads it may create new tumors in different organs of the body. Breast cancer that metastasizes in the lung, however, is still called breast cancer, not lung cancer.

    Unknown Primary Sites

    • According to the National Cancer Institute, 2 to 4 percent of all cancers have an unknown primary site. These are called cancer of an unknown primary, or CUP. Current technology can sometimes assist a doctor in tracing the cancer back to a primary site, but not always. CUPs can make diagnosis and treatment more difficult.

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