Tamoxifen, also known by its brand name Nolvadex, is an antiestrogen drug that has been used for over 30 years in the treatment of early-stage and metastatic breast cancer. It's an oral medicine given in pill form. Tamoxifen is also used in prevention of breast cancer in women at high risk of developing the disease.

Estrogen can stimulate the growth of certain breast cancer cells. Tamoxifen works to block estrogen to keep that from happening.

Even though tamoxifen is an antiestrogen drug, it has the ability to act like estrogen in other cells of the body besides the breasts.  Therefore, other body tissue isn't completely deprived of estrogen.

The most common side effects of tamoxifen resemble those of menopause including hot flashes, irregular periods and vaginal discharge. Women and men who take the drug may have headaches, nausea, vomiting and fatigue. Men may also experience impotence.

• Uterine: An increased risk of developing uterine cancers is the most serious side effect of tamoxifen use for invasive breast cancer. According to the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-14 Study, the average rate of endometrial cancer developing in women within 5 years of treatment of tamoxifen was 1.2 in 1000. The survival rate of women who developed endometrial cancer after taking tamoxifen was 38% less than those who took the placebo.
• Clots and Stroke: Other serious side effects include blood clots and stroke. The NSABP P-1 study showed an elevated risk of stroke and deep vein thrombosis in women 50 and older.
• Pregnancy: Women are advised not to become pregnant while on the drug due to potential damage to the fetus.
• Eyes: There is a possibility of patients being at an increased risk of developing cataratcs, corneal scarring and retinal changes.

The listing of side effects is not meant to discourage you from taking tamoxifen. Each case will be different. Your doctor will tell you if tamoxifen is the right cancer therapy for you.

Tamoxifen is generally prescribed for 5 years for people with early-stage breast cancer and for those who are using it along with other cancer treatments. It's important to discuss any concerns you have about the length of treatment and side effects with your doctor.

Sources consulted:

• National Surgical Adjuvant Breast and Bowel Project (NSABP) B-14 Study.
• National Surgical Adjuvant Breast and Bowel Project (NSABP) P-1 Study.
• Tamoxifen: Q & A. U.S. National Institutes of Health: National Cancer Institute. 3/17/08. 8/2009 (accessed).