National Surgical Adjuvant
Breast and Bowel Project, Operations Center, Pittsburgh,
PA, USA.
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.
