Key Statistics for Cancers of Unknown Primary
How common are cancers of unknown primary?
The exact number of people diagnosed with cancers of unknown primary (CUP) each year is unknown. This is because some cancers start out being diagnosed as an unknown ( or unspecified) primary, but the primary site is found later.
The American Cancer Society estimates that about 37,370 cases of cancer of unknown primary will be diagnosed in 2025 in the United States:
- About 19,720 will be diagnosed in men
- About ?17,650 will be diagnosed in women.
This number represents about 2% of all cancers.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
American Cancer Society. Facts & Figures 2025. American Cancer Society. Atlanta. 2025.
Bochtler T, L?ffler H, Kr?mer A. Diagnosis and management of metastatic neoplasms with unknown primary. Semin Diagn Pathol. 2018 May;35(3):199-206. doi: 10.1053/j.semdp.2017.11.013. Epub 2017 Nov 26. PMID: 29203116.
Howlader N, Noone AM, Krapcho M, et al (eds). SEER Cancer Statistics Review, 1975-2014, National Cancer Institute. Bethesda, MD, https://seer.cancer.gov/csr/1975_2014/, 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. 础产别濒辞蹿蹿’蝉 Clinical Oncology. 5th ed. Philadelphia, PA. Elsevier: 2014:1792-1803.
Last Revised: May 27, 2025
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