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Supporting Evidence

The current standard of treatment offered to high risk patients would be tamoxifen 20mg/daily taken orally, for five consecutive years, as per the National Surgical Breast and Bowel Project (NSABP) P-1 clinical trial (13,14).

Other tamoxifen prevention trials have also been reported in the past, such as the Royal Marsden Hospital study (15,16), the Italian Tamoxifen Prevention study (8,9), and the first International Breast Cancer Intervention study (IBIS-1) (17,18), but the NSABP P-1 has historically been recognized as the landmark trial proving tamoxifen to be an effective chemopreventative agent.

The conclusion reached from this trial suggests that tamoxifen reduces the risk of invasive breast cancer by 49% compared to placebo. The Early Breast Cancer Trialists’ meta-analysis confirmed that the risk of contralateral primary breast cancer is substantially reduced by 5 years of tamoxifen therapy in women with first breast cancers that are estrogen receptor-positive or have an unknown estrogen receptor status (19).

An alternative to tamoxifen for postmenopausal women is raloxifene 60mg/daily, taken orally, for five consecutive years, as per the STAR trial (Study of Tamoxifen and Raloxifene) (20,21). This trial concluded that raloxifene is as effective as tamoxifen in reducing the risk of invasive breast cancer.

Also, findings suggest that though the risk of thromboembolic events and cataracts exist with both SERMs, the risk appears to be less for raloxifene. However, raloxifene did not reduce the risk of developing ductal carcinoma insitu (DCIS) in the STAR trial. Both of these drugs have received FDA approval for use in chemoprevention of breast cancer.
Another alternative for postmenopausal patients is exemestane 25mg/daily, taken orally, for five consecutive years as per the recently published NCIC CTG MAP.3 clinical trial (12). In this large chemoprevention trial, 4560 women were randomly assigned to exemestane or placebo. At a median follow-up of 35 months, there was a 65% relative reduction in the annual incidence of invasive breast cancer in the exemestane arm compared to the placebo arm. No significant differences were noted between the two arms in terms of skeletal fractures, cardiovascular events, other cancers, or treatment-related deaths.
The consultation with the medical oncologist will also include a thorough discussion with the patient of the known side effects of tamoxifen, raloxifene, or exemestane to allow the patient to make a fully informed treatment decision.


Updated Jul 12, 2012