Skip to main content

Hormone Therapy for a Cancer of Unknown Primary

Some types of cancer grow in response to sex hormones in the body. For example, most breast cancers have proteins called estrogen receptors and/or progesterone receptors on the surface of their cells. These cancers grow faster when exposed to the hormone estrogen. Likewise, most prostate cancers grow in response to male hormones called androgens, such as testosterone.

In cases where a cancer of unknown primary (CUP) is likely to be a breast or prostate cancer, hormone therapy may be an effective way to slow the growth of the cancer, or perhaps even shrink it, and may help you live longer.

For breast cancer, types of hormone therapy include drugs like tamoxifen, toremifene (Fareston), fulvestrant (Faslodex); LHRH agonists like leuprolide (Lupron) and goserelin (Zoladex); and the aromatase inhibitors anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin). These drugs either lower estrogen levels or prevent cancer cells from being able to use it. For more information on how these drugs are used and their potential side effects, see Hormone Therapy for Breast Cancer.

Hormone therapy can also be used to treat prostate cancer. Some commonly used drugs include LHRH agonists such as leuprolide (Lupron, Eligard), goserelin (Zoladex), and triptorelin (Trelstar), and anti-androgens such as flutamide (Eulexin), bicalutamide (Casodex), enzalutamide (Xtandi), and apalutamide (Erleada). These drugs either lower the testosterone level or prevent cancer cells from being able to use it. Surgery to remove the testicles (orchiectomy) is another option. For more information, see Hormone Therapy for Prostate Cancer.

More information about hormone therapy

To learn more about how hormone therapy is used to treat cancer, see Hormone Therapy.

To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.

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.

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].

Greco FA, Hainsworth JD. Carcinoma of Unknown Primary In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia, PA: Lippincott Williams & Wilkins 2015: 1719-1736.

National Cancer Institute. Physician Data Query (PDQ). Cancer of Unknown Primary Treatment. 07/25/2015. Accessed at: on February 9, 2018.

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Occult Primary. v.1.2018. Accessed at on February 9, 2018.

Tomuleasa C, Zaharie F, Muresan MS, Pop L, Fekete Z, Dima D, Frinc I, Trifa A, Berce C, Jurj A, Berindan-Neagoe I, Zdrenghea M. How to diagnose and treat a cancer of unknown primary site. J Gastrointestin Liver Dis. 2017 Mar;26(1):69-79. doi: 10.15403/jgld.2014.1121.261.haz.

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: September 23, 2021

American Cancer Society Emails

Sign up to stay up-to-date with news, valuable information, and ways to get involved with the American Cancer Society.