How2Day: Tamoxifen Studies

As of 2010, BREASTCANCER.org reports that approximately one in eight American women will be diagnosed with breast cancer during her lifetime. Due to a greater understanding of the disease and improvements in treatment methods and drug therapies, BREASTCANCER.org also reports that the death rate for breast cancer has been steadily declining since 1991. The drug Tamoxifen is one example of such drug therapies. According to Drugs.com, Tamoxifen works by blocking the estrogen required for the growth of certain types of breast cancer. Tamoxifen and its short and long-term effects have been the subject of several current studies.

According to the National Cancer Institute (NCI), the Breast Cancer Prevention Trial (BCPT) was conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP) and funded by NCI. The purpose of BCPT was to determine whether tamoxifen could prevent breast cancer development in high risk women. Beginning in 1992, 13,338 women at high risk for developing breast cancer were divided into two groups, with one group receiving tamoxifen and one group receiving a placebo, daily for five years. When the trial ended in 1997, the results listed 49 percent fewer cases of invasive breast cancer and 49 percent fewer cases of noninvasive tumors among the women receiving tamoxifen. The results were published in 1998, leading to tamoxifen's FDA approval. NCI reports that side effects found during the study included an increased risk for endometrial and uterine cancers, stroke, and blood clots in the lungs and large veins.

NCI reports that the participants of the original BCPT continued to be studied throughout seven years of follow-up appointments. At this seven-year mark, NCI noted there were 43 percent fewer diagnoses of invasive breast cancers and 27 percent fewer diagnoses of noninvasive breast tumors. The risks of strokes and blood clots were slightly decreased at this point as well.

In the 1999 Study of Tamoxifen and Raloxifene (STAR), also conducted by NSABP in partnership with NCI, 19,000 post-menopausal women were divided into two groups. According to NCI, one group received tamoxifen and the other group received another estrogen-blocking drug, raloxifene, every day for five years. Results from the study, which ended in 2004, indicate that both drugs reduced the risk of invasive tumors by 50 percent, but raloxifene did not reduce the risk for noninvasive tumors. NCI reported that raloxifene received FDA approval in 2007 to treat invasive breast cancers in postmenopausal women. In the group taking raloxifene, NCI reported reduced risk of endometrial cancer and blood clotting.

According to its website, the International Breast Cancer Intervention Study (IBIS-I) enrolled 7,154 European women considered to be at a high risk of developing breast cancer. According to NCI, half the women were given tamoxifen and half were given placebo for 50 months. The IBIS-I website reported a 32 percent reduction in invasive breast cancers during the course of tamoxifen treatment. IBIS-I also reported increased occurrences of endometrial cancer and blood clots during the course of active tamoxifen treatment. Women participating in IBIS-I were studied throughout 96 months of follow-up treatment. During this period, IBIS-I reported that tamoxifen continued to reduce the occurrence of invasive breast cancers by 32 percent in the first five years after treatment and 18 percent in the following years.

Barts and the London School of Medicine and Dentistry are enrolling women in the Second International Breast Cancer Intervention Study (IBIS-II). In this study, tamoxifen will be compared to the drug anastrozole to determine which drug is more effective at preventing ductal carcinoma in situ (DCIS), an early form of breast cancer affecting the milk ducts. According to the IBIS-II website, the study plans to recruit at least 4,000 women by December 2010. Half of the participants will be taking tamoxifen and a placebo each day, and the other half of the participants will be taking anastrozole and a placebo each day, for five years. The site reports that the first set of results are expected to be published in 2012.

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