[Jackie07]

From Cancer.org:

Hormone therapy is another form of systemic therapy. Like chemotherapy, hormone therapy can be used either as an adjuvant therapy to help reduce the risk of cancer recurrence after surgery or when the cancer has become metastatic.

Some breast cancers grow in response to the hormone estrogen. Estrogen is usually thought of as a "female" hormone, but men have it in their bodies as well, just at lower levels. About 9 out of 10 breast cancers in men have hormone receptors on the surface of their cells -- that is, their cancers are estrogen receptor (ER)-positive and/or progesterone receptor (PR)-positive. This makes them more likely to respond to hormone treatments. Hormone therapy does not help patients whose tumors are both ER- and PR-negative.

Several approaches to blocking the effects of estrogen or lowering estrogen levels are used to treat breast cancer in women. While many of these may work in men as well, doctors have the most experience with using anti-estrogen drugs such as tamoxifen in men.
In the metastatic setting, hormonal treatments are often used in a sequence. For example, tamoxifen may be tried first. If the cancer does not respond or if it grows back after an initial response, other hormonal treatments may be tried.

Tamoxifen: Tamoxifen works by blocking the estrogen receptors on cancer cells, which prevents estrogen from spurring their growth. It is taken daily in pill form, usually for 5 years, to reduce the chances of the cancer coming back after surgery. Tamoxifen can also be used to treat advanced breast cancer.

The most common side effects include fatigue, hot flashes, and sexual problems. A rare but more serious side effect is blood clots, which usually form in deep veins of the leg. In some cases, this increased risk of clotting may lead to a heart attack, stroke, or blood clots spreading to the lungs (pulmonary embolism). Call your doctor or nurse right away if you develop pain, redness, or swelling in your lower leg (calf), shortness of breath, chest pain, sudden severe headache, confusion, or trouble speaking or moving.

Aromatase inhibitors: This group of drugs includes anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin). They block the production of small amounts of estrogen by the adrenal glands. They are taken daily as pills. They have been found to be very effective in treating breast cancer in women, but they have not been well studied in men. Still, some doctors use them as the first line of hormone therapy instead of tamoxifen. Clinical trials are also under way to look at using aromatase inhibitors along with LHRH analogs (see below).

The main side effects of these drugs are thinning of the bones and joint stiffness.