Tamoxifen has been used for years to treat breast cancer. More recently, tamoxifen has been used to prevent breast cancer in patients with breast disease and those at high risk of developing breast cancer. However, tamoxifen is only useful in patients whose breast cancer is estrogen-receptor positive. Tamoxifen can modify the action of estrogen, which can result in adverse effects. It can add to the risk of getting certain cancers for post-menopausal women.
How Tamoxifen Works
Estrogen can make some breast cancer cells grow. It can bind to special proteins on the cells' surface and cause them to divide and increase in number. Tamoxifen binds to these specialized proteins and prevents these cells from dividing. Therefore, it's only effective in breast cancers that are estrogen-receptor positive.
Cancer Risks
Tamoxifen has been found to increase the risk of certain cancers, especially in post-menopausal women. A study in the January 2003 issue of The Lancet showed that tamoxifen could double the rate of endometrial cancer, though the endometrial cancer was often found at an early stage and successfully treated. Uterine sarcoma, another cancer, can also increase with tamoxifen use.
Blood Clots
The 2007 February issue of the Journal of National Cancer Institute showed that patients on Tamoxifen had a two-fold increase risk of thromboembolic events--in other words, developing blood clots. The most common incidences were blood clots in the lung, pulmonary emboli, deep vein thrombosis and blood clots in the eye, known as retinal vein thrombosis.. This increased risk occurred only while the patient was on tamoxifen. Tamoxifen has also been associated with an increased risk of strokes, especially in women older than 50.
Bone Loss
A study in the November 2005 issue of the Journal of the National Cancer Institute reviewed bone fractures in women on tamoxifen. Women on tamoxifen showed a reduction in bone breaks by 32 percent compared to those on placebos. Those who did suffer fractures on tamoxifen were women older than 50. A study published in the Journal of Clinical Oncology in 1996 looked at women who were premenopausal and on tamoxifen, and found they showed less bone loss than those on placebos.
Cataracts
A review published in the July 2009 issue of the Journal of Clinical Oncology examined a number of studies for the incidence of cataracts as well as other adverse effects. They found that those on tamoxifen showed an increased risk of cataracts and for the need to have cataract surgery.
Benefits
Tamoxifen has been used for many decades. There are a number of follow-up studies for the patient to be able to make informed decisions regarding its use. Tamoxifen has been found to be effective in reducing the recurrence of invasive breast cancer in estrogen receptor-positive breast cancers. This benefit was seen even two years after completing a five-year course of tamoxifen. It has also been shown that tamoxifen can reduce high-risk patients from developing breast cancer.
References
- " The Lancet"; Overview of the Main Outcomes in Breast Cancer Prevention Trials; J. Cuzick, et al; January 2003
- "Journal National Cancer Institute"; Long-term Results of Tamoxifen Prophylaxis for Breast-Cancer-96 Month Follow-Up of the Randomized IBIS-I Trial; J. Cuzick, et al; February 2007
- "Journal National Cancer Institute"; Tamoxifen for the Prevention of Breast Cancer: Current Status of the National Surgical Adjuvant Breast and Bowel Project P-1 Study; B. Fisher et al; November 2005
- " Journal of Clinical Oncology"; Effect of Tamoxifen on Bone Mineral DensityMeasured by Dual-Energy X-ray Absorptiometry in Healthy Pre-Menopausal and Post-Menopausal Women; T.J. Powles, et al; January 1996
- "Journal of Clinical Oncology"; ASCO Clinical Practice Guideline Update on the use of Pharmacologic Interventions Including Tamoxifen, Raloxifene, and Aromatase Inhibition for Breast Cancer Risk Reduction; K. Visvanathan, et al; July 2009
