The exact number of cancers of unknown primary (CUP) diagnosed each year is unknown, because some cancers start out being diagnosed as unknown primary, but the primary site is found later. Still, the American Cancer Society estimates that about 32,590 cases of cancer of unknown primary will be diagnosed in 2023 in the United States. This number represents about 2% of all cancers. As more sophisticated lab tests become available to determine where a cancer started, the number of cancers of unknown primary may go down.
Visit the American Cancer Society’s Cancer Statistics Center for more key statistics.
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American Cancer Society. Facts & Figures 2023. American Cancer Society. Atlanta, Ga. 2023.
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Last Revised: January 12, 2023