Duration of adjuvant tamoxifen therapy.

The benefit of using adjuvant tamoxifen to treat breast cancer has been firmly established for patients with estrogen receptor (ER)-positive tumors, regardless of age, lymph node status, or menopausal status. Uncertainty remains, however, regarding the optimal duration of tamoxifen therapy. We reviewed the findings of randomized clinical trials that directly compared alternative treatment durations. Trials comparing short-term adjuvant treatment with tamoxifen (i.e., 1-3 years) with treatments having durations of about 5 years consistently have demonstrated additional benefits stemming from the longer therapy. Trials testing 5 years of treatment with longer durations have, in the aggregate, suggested no additional benefit for the patient. Nevertheless, the number of recurrences reported to date in these trials is not large, and the results of the individual trials are heterogeneous. Furthermore, as a result of tamoxifen's "carryover" effect, duration trials require considerable follow-up before definitive results can be established. Until more definitive data become available, adjuvant treatment with tamoxifen should be limited to 5 years outside the clinical trials setting. Continued accrual of ER-positive patients to ongoing tamoxifen duration trials, including the Adjuvant Tamoxifen Treatment Offer More (aTTom) and Adjuvant Tamoxifen Longer Against Shorter (ATLAS) trials, is appropriate. Alternatively, patients who remain disease free after 5 years of tamoxifen therapy should be encouraged to participate in trials testing crossover to other hormonal interventions, including selective ER modulators or aromatase inhibitors.