Hormone Therapy for a Cancer of Unknown Primary

Some types of cancer grow in response to hormones in the body. 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.

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.

If the unknown primary is a breast cancer

For breast cancer, types of hormone therapy include drugs like tamoxifen, toremifene (Fareston), fulvestrant (Faslodex); LHRH agonists like leuprolide (Lupron) and goserelin (Zoladex); and aromatase inhibitors like 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.

If the unknown primary is a prostate 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.