PDFs by language
Our 24/7 cancer helpline provides support for people dealing with cancer. We can connect you with trained cancer information specialists who will answer questions about a cancer diagnosis and provide guidance and a compassionate ear.
Chat live online
Select the Live Chat button at the bottom of the page
At our National Cancer Information Center trained Cancer Information Specialists can answer questions 24 hours a day, every day of the year to empower you with accurate, up-to-date information to help you make educated health decisions. We connect patients, caregivers, and family members with valuable services and resources.
Or ask us how you can get involved and support the fight against cancer. Some of the topics we can assist with include:
For medical questions, we encourage you to review our information with your doctor.
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.
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 journalists, editors, and translators with extensive experience in medical writing.
American Cancer Society. Facts & Figures 2023. American Cancer Society. Atlanta, Ga. 2023.
Bochtler T, Löffler H, Krämer A. Diagnosis and management of metastatic neoplasms with unknown primary. Semin Diagn Pathol. 2017 Nov;26(pii). doi: 10.1053/j.semdp.2017.11.013. [Epub ahead of print].
Howlader N, Noone AM, Krapcho M, Miller D, Bishop K, Kosary CL, Yu M, Ruhl J, Tatalovich Z, Mariotto A, Lewis DR, Chen HS, Feuer EJ, Cronin KA (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 web site, 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: January 12, 2023
American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.