NEW YORK (Reuters Health) Dec 11 - Breast cancer recurrence rates are lower with aromatase inhibitors than with tamoxifen, according to meta-analyses published online by the Journal of Clinical Oncology.
Furthermore, recurrence is reduced whether the aromatase inhibitors are given initially or after several years of tamoxifen therapy, the researchers report.
Dr. Mitch Dowsett, from Royal Marsden Hospital in London, UK, and members of the Early Breast Cancer Trialists' Collaborative Group analyzed data from six trials involving nearly 19,000 women, all of whom had estrogen-receptor positive tumors.
The trials were grouped into two cohorts. Cohort 1 included 9,856 enrollees in two 5-year trials that compared aromatase inhibitors with tamoxifen, with each drug started immediately after surgery.
Cohort 2 comprised 9,015 participants in four 5-year trials in which all women started on tamoxifen after surgery. After two to three years, some were switched to aromatase inhibitors for the remainder of the study, and the rest continued with tamoxifen.
In the first cohort, aromatase inhibitor therapy led to an absolute decrease in recurrence of 2.9% (9.6% for aromatase inhibitors vs 12.6% for tamoxifen; 2p <>
In the second cohort, at 3 years from treatment divergence (approximately 5 years after starting hormonal therapy), aromatase inhibitors were associated with an absolute 3.1% decrease in recurrence (5.0% vs 8.1%, 2p < 2p =" 0.02).
"When the switch to an aromatase inhibitor is made after 2 to 3 years of tamoxifen, there seems to be a particularly marked reduction in risk of recurrence (by 40%) during the following 3 years," the authors comment. They also note that aromatase inhibitors were not associated with any increase in non-breast cancer deaths relative to tamoxifen.
On the other hand, the adverse effect profile differs between the two classes of drugs. Aromatase inhibitors are associated with fewer endometrial cancers and thromboembolic events than the selective estrogen receptor modulator, but with more arthralgia and fractures.
"The decision on whether to initiate treatment with an aromatase inhibitor or tamoxifen or whether to switch to an aromatase inhibitor after 2 to 3 years of tamoxifen rather than continuing with tamoxifen for 5 years depends on a careful evaluation of these factors in individual patients," Dr. Dowsett and his associates maintain.
They conclude: "This overview has provided greater confidence in the efficacy aspects of this evaluation."
J Clin Oncol 2009.