Adherence to endocrine therapy for breast cancer

Purpose: Despite the demonstrated efficacy of long-duration adjuvant tamoxifen and aromatase inhibitor use in breast cancer management, information on adherence to such therapy is limited. Therefore, we reviewed the published literature regarding hormonal therapy adherence in clinical trial and practice settings. Methods: A systematic search of the PubMed database, augmented by a review of manuscript references and conference proceedings, commonly identified adherence reports in clinical trials but identified only 9 adherence reports in clinical practice settings. Results: In adjuvant breast cancer clinical trials with longer (>= 4 years) follow-up, hormonal therapy (tamoxifen or aromatase inhibitors) was prematurely discontinued by about 23-28% of the study participants. Adherence to aromatase inhibitors did not differ from adherence to tamoxifen in this setting. In breast cancer prevention trials, tamoxifen was prematurely discontinued by 20-46% of the participants. In clinical practice settings, only 2 reports addressed longer-duration (> 4 years) adherence to adjuvant tamoxifen use. In these, tamoxifen was prematurely discontinued by 30-50% of the patients. Conclusion: Adherence to prescribed breast cancer hormone therapy has not received concerted attention. Current, albeit limited, evidence suggests long-term hormone therapy adherence may represent an area limiting optimal breast cancer patient treatment.