Based on 2 meta-analyses of nearly 20,000 HR+ early breast cancer patients, AIs are superior to tamoxifen in reducing recurrences, whether as initial monotherapy or given in a “switching” strategy (abstract 12). As initial monotherapy, AIs reduced the risk of recurrence by 23% over tamoxifen; for patients who switched to AIs after 2–3 yr of tamoxifen, AIs reduced the risk by 29%, relative to those who continued on tamoxifen, James Ingle, MD, reported.
The study was based on data submitted to the Early Breast Cancer Trialists’ Collaborative Group from 6 major trials. In cohort 1 (n = 9,856), patients receiving endocrine monotherapy (tamoxifen or an AI alone for a total of 5 yr), recurrences were seen in 15.3% of AI users at 8 yr post-diagnosis, vs 19.2% of tamoxifen users (P < .00001).
“Compared with tamoxifen, AI monotherapy was associated with a highly significant absolute gain of 2.9% at 5 yr and 3.9% at 8 yr of patients who remained free of breast cancer recurrence,” Dr. Ingle said. AI use was associated with a decrease in breast cancer mortality of 1.1% at 5 yr and 0.5% at 8 yr compared with tamoxifen but this was not statistically significant.
Cohort 2 (n = 9,015) involved patients who, aft er 2–3 yr of tamoxifen, were randomized to continue tamoxifen for a total of 5 yr or to switch to an AI to complete their 5 yr of adjuvant endocrine therapy. At 6 yr post-randomization, breast cancer recurred in 12.6% of those switched to an AI vs 16.1% of those who continued on tamoxifen. The overall comparison of time to recurrence was highly significant (P < .00001).
Breast cancer mortality was significantly reduced with the use of AIs in the switching cohort, yielding an absolute reduction of 0.7% at 3 yr and 1.6% at 6 yr from treatment divergence.
Patients saw the most differential benefit from AIs while still on therapy vs after discontinuation. “There is a change when patients go off therapy, but AIs are still better,” Dr. Ingle noted. “AI treatment duration is now a major question to be answered.”