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Cancer of unknown primary (CUP) affects 2 in 100 people diagnosed with cancer in the UK (2%). It can affect people of all ages, but is most common in people aged 60 or over.
Cancer of unknown primary means your doctor is not sure where the cancer started. They have found a secondary cancer but have not been able to find the primary cancer. People with CUP sometimes have more than one secondary cancer. We have more information about secondary cancer.
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