Tamoxifen is a chemoprevention agent used to reduce the risk of breast cancer. In 1998, the U.S. Food and Drug Administration (FDA) approved the use of tamoxifen for breast cancer risk reduction in women with a five-year risk of breast cancer greater than 1.67 percent. However, despite its therapeutic effects for breast cancer and a number of diseases such as bipolar disorder and infertility, tamoxifen has been linked to a number of long-term side effects, including increased risks of venous thromboembolism, cataracts and endometrial cancer. These serious adverse effects are distinguished from short-term side effects such as weight gain, changes in periods, hot flashes and nausea, which will disappear if patients discontinue tamoxifen therapy.
Formation of Blood Clots
Long-term use of tamoxifen has been shown to increase risk of developing blood clots. Blood clots often occur in the veins of the legs, referred to as deep vein thrombosis.
In rare cases, blood clots can form in blood vessel in the heart or the brain. Consequently, tamoxifen therapy has been associated with increasing risk of stroke, heart attacks and pulmonary embolism. Pulmonary embolism occurs when a blood clot in the vein dislodges and migrates to the lungs.
Endometrial Cancer
Use of tamoxifen is associated with an increased risk of endometrial cancer. Endometrial cancer starts in the lining of the womb (uterus). Women who use tamoxifen are to to three times more likely to develop endometrial cancer than those who do not.
Cataracts
Long-term use of tamoxifen is associated with an increased risk of cataracts (the clouding of the eyes' lenses). Cataracts affect a person's ability to see clearly. Data from a breast cancer prevention study published in a 2009 issue of the "Journal of the National Cancer Institute" showed that tamoxifen increases the risk of developing cataracts by 15 percent, but most importantly, tamoxifen increases the risk of having surgery for cataracts by 55 percent. That is, tamoxifen increases the risk of developing cataracts that require surgery.
References
- "Journal of Clinical Oncology"; Technology assessment on breast cancer risk reduction strategies: tamoxifen and raloxifene; Chlebowski R.T., Collyar D.E., Somerfield, M.R., et al.; May 2002
- "Journal of the National Cancer Institute"; Value of adding single-nucleotide polymorphism genotypes to a breast cancer risk model; M.H. Gail; July 2009
- "Journal of the National Cancer Institute"; Cuzick J., Forbes J.F., Sestak I., et al.; Long-term results of tamoxifen prophylaxis for breast cancer--96-month follow-up of the randomized IBIS-I trial; February 2007
