Breast Cancer Treatments

In most women, the primary course of therapy for breast cancer is surgery. However, for certain types of cancer or for cancer in specific stages of development, radiation or breast cancer drugs may be used to halt the progression of the disease and, in some cases, achieve death of the tumor cells. Breast cancer treatments for early-stage breast cancer, for example, may include administration of certain breast cancer medications prior to using surgery, and most breast cancer patients undergo medication treatment following surgery to ensure all of the breast cancer cells have been eliminated.

Breast cancer drugs are generally better tolerated than radiation, and have risen steadily in popularity over the years as a result. Today, there are several breast cancer drugs on the market, including tamoxifen, Arimidex, Aromasin and Femara.

Many breast cancers are dependent upon the production and availability of estrogen. As a result, breast cancer medications are used to inhibit the cells’ use of estrogen, or prevent the production of the hormone.

Tamoxifen

Among breast cancer medications, tamoxifen is a popular choice for treatment of early-stage breast cancer. The drug is an antagonist of the estrogen receptor gene in breast tissue, competitively binding to these receptors on tumors located in the breast. Once metabolized in the liver, tamoxifen’s metabolites are incorporated by these receptors, interfering with the DNA of tumor cells and preventing them from developing into stages where they can reproduce. Because these metabolites keep cells from moving into the next stage of reproductive development instead of actually killing the cancer cells, they are considered cytostatic rather than cytocidal.

Discovered in the 1950s, it was not until 1980, when clinical trial results revealed the efficacy of tamoxifen in treating breast cancer, that the drug became widely used for the treatment of early breast cancer. Doubts about its actual benefit persisted until a meta-analysis performed in 1998 proved the drug does definitively improve survival rates among women with early-stage breast cancer.

Tamoxifen is associated with certain side effects, including bone loss prevention in postmenopausal women. By preventing the development of osteoclasts, cells that cause the mineral breakdown of bone tissues, tamoxifen helps prevent osteoporosis in these women. Interestingly, the drug has been associated with increased bone loss in women who are pre-menopausal.

Tamoxifen has also been associated with an increased risk of endometrial cancer, acting as an agonist on uterine tissues.

Arimidex

Arimidex is the trade name for the drug anastrozole, an agent which is one of the more common breast cancer medications used in the post-surgical treatment of breast cancer, as well as for the treatment of metastases related to breast tumors. Arimidex works by inhibiting the production of the hormone estrogen, which is essential for the development of certain types of breast cancers. The drug acts by preventing the release of aromatase, an enzyme that is used to convert androgen steroids into estrogen. By preventing the release of the enzyme, the formation of estrogen is prevented and cancer cell development that relies on the hormone is halted.

Arimidex is often preferred for the treatment of localized breast cancer in postmenopausal women as a result of clinical trials which showed an overall advantage of the drug over tamoxifen in that population.

The primary side effect of Arimidex is bone weakness, and in a side-by-side comparison, women treated with Arimidex were more than twice as likely to suffer bone fractures as those who were treated with tamoxifen. As a result, often this drug is prescribed along with a statin medication, to help prevent bone loss.

Aromasin
Another of the more common breast cancer medications, Aromasin (exemestane) works on the same principle as Arimidex, preventing the transformation of androgens into estrogens. However, Aromasin’s mechanism of action is different. While Arimidex prevents the release of the enzyme aromatase, an enzyme essential for transforming androgen into estrogen, Aromasin “tricks” aromatase into incorporating it during its production phase. Once Aromasin is incorporated into the enzyme’s structure, it prevents it from interacting with androgens, thereby preventing the formation of estrogen.

Like Arimidex, Aromastin is also associated with a higher risk of osteoporosis and fracture than tamoxifen. Stains may also be prescribed to help offset these risks.

Femara

Femara is the trade name for the drug letrozole, an oral medication that also acts on the aromatase enzyme. Like Arimidex and Aromasin, Femara is used in breast cancer treatments in patients whose cancer is responsive to hormonal inhibition.

Femara binds to a specific location in the aromatase enzyme, called the cytochrome P450 unit, and acts to prevent the enzyme from successfully converting androgens to estrogens. Femara is recommended for the treatment of early-stage breast cancer in postmenopausal women.

Like the other aromatase inhibitors, Femara is also associated with an increased risk of fracture and osteoporosis, and may be prescribed along with a statin to reduce these risks.