Key Statistics for Cancers of Unknown Primary

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 31,810 cases of cancer of unknown primary will be diagnosed in 2018 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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Our team is made up of doctors and master's-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

American Cancer Society. Facts & Figures 2018. American Cancer Society. Atlanta, Ga. 2018.

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Mnatsakanyan E, Tung WC, Caine B, Smith-Gagen J. Cancer of unknown primary: Time trends in incidence, United States. Cancer Causes Control. 2014 Jun;25(6):747-57. doi: 10.1007/s10552-014-0378-2. Epub 2014 Apr 8.

Varadhachary GR, Lenzi R, Raber MN, Abbruzzese JL. Carcinoma of Unknown Primary In: Neiderhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 5th ed. Philadelphia, PA. Elsevier: 2014:1792-1803.

Last Medical Review: March 9, 2018 Last Revised: March 9, 2018

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