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Key Statistics for Cancers of Unknown Primary

How common are 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 34,950 cases of cancer of unknown primary will be diagnosed in 2024 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.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.


American Cancer Society. Facts & Figures 2024. American Cancer Society. Atlanta. 2024.

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Howlader N, Noone AM, Krapcho M, et al (eds). SEER Cancer Statistics Review, 1975-2014, National Cancer Institute. Bethesda, MD,, based on November 2016 SEER data submission, posted to the SEER website, April 2017.

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 Revised: May 27, 2024

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