Tamoxifen--an update on current data and where it can now be used.

Over the past 30 years, data from a large number of clinical trials have confirmed the efficacy of tamoxifen in estrogen receptor (ER)-positive breast cancer, both as adjuvant therapy and for advanced disease. The 1995 Early Breast Cancer Trialists' Collaborative Group (EBCTCG) overview of randomized trials of adjuvant tamoxifen versus no tamoxifen showed that during approximately 10 years of follow-up, the proportional reductions in mortality for 1, 2 and approximately 5 years of adjuvant tamoxifen were 12, 17 and 26%, respectively. Tamoxifen is also effective for the prevention of breast cancer. In the National Surgical Adjuvant Breast and Bowel Project (NSABP) breast cancer prevention study (P-1), 5 years of tamoxifen therapy reduced the incidence of invasive and non-invasive breast cancers by 49 and 50%, respectively. In a randomized NSABP trial in women with ductal carcinoma in situ (DCIS), tamoxifen brought about a significant 47% reduction in ipsilateral invasive breast cancers and a 15% reduction in non-invasive breast cancers, compared with placebo. In trials performed by the Swedish Breast Cancer Co-operative Group and the NSABP, the optimal duration of adjuvant tamoxifen therapy appears to be 5 years, although this is equivocal and not yet conclusively defined.