Tamoxifen helps prevent breast cancer

A recent study has confirmed that tamoxifen can reduce the risk of breast cancer in healthy women during the active treatment phase. Earlier three clinical trials on the use of tamoxifen to prevent breast cancer had reported mixed results. The overall evidence supports a reduction in the risk of breast cancer, but whether this benefit outweighs the risks and side effects associated with tamoxifen was still unclear. The researchers from the IBIS Trials Centre, Cancer Research UK took up this study. They carried out a placebo-controlled randomised trial of tamoxifen, in 7152 women aged 35-70 years, who were at increased risk of breast cancer. They were randomly assigned 5 years of treatment with tamoxifen 20 mg/day or matching placebo. Women were recruited through attendance at family history clinics, relatives of women with breast cancer, breast screening centres, general practitioners, and the media. Analyses were by intention to treat after exclusion of 13 women. Reasons for exclusion were any previous invasive cancer, a previous deep vein thrombosis or pulmonary embolism, current use of anticoagulants, or a life expectancy judged to be less than 10 years. Women who were pregnant or wished to become pregnant were also excluded. Women were followed up every 6 months during the 5 years of active treatment and by annual questionnaire or clinical visits. Details of any side effects were collected at every visit. Symptoms, diagnoses, and procedures were each recorded separately and all concomitant medications were recorded. Mammography was done every 12-18 months, and blood samples were requested again at 1 year and 5 years. After a follow-up of 50 months, 69 breast cancers had been diagnosed in 3578 women in the tamoxifen group and 101 in 3566 in the placebo group (risk reduction 32%). This 32% reduction in risk seen in the study is consistent with the cumulative results when all of the trials are combined. Age, degree of risk, and use of hormone-replacement therapy did not affect the reduction. It was found that tamoxifen reduces the risk of breast cancer by about a third. Temporary cessation of tamoxifen should be considered and the use of appropriate antithrombotic measures is recommended during and after major surgery or periods of immobilisation. When used as a therapy for breast cancer, tamoxifen can clearly reduce the risk of recurrence and death. The combined evidence indicates that mortality from non breast cancer causes is not increased by tamoxifen. The overall risk to benefit ratio for the use of tamoxifen in prevention is still unclear. Further long-term follow up to study breast cancer incidence and mortality, other causes of death, and side effects in the current trials remains essential.