The UZ Leuven Policy for Extended Adjuvant Anti-estrogen Therapy in Women With Early Estrogen Receptor-Positive Breast Cancer

Five years after adjuvant endocrine treatment for estrogen receptor (ER)-positive breast cancer, patients have a 2 to 20 % risk of metastatic relapse during the next 5 years. Extended adjuvant endocrine therapy seems to further lower this. In UZ Leuven, extended endocrine therapy is now discussed unless the tumor was a grade 1–2, pT1N0, ER-positive, progesterone receptor (PR)-positive, HER2-negative lesion. After 5 years of adjuvant tamoxifen treatment for ER-positive breast cancer, we encourage women to take another 5 years of tamoxifen. If the tumor was lymph node-positive at diagnosis and patients are menopausal after the first 5 years of tamoxifen, we advise to take prolonged treatment with an oral aromatase inhibitor (AI). For this particular group, available data for extending endocrine therapy with an AI after 5 years of tamoxifen are strongest and more convincing for letrozole than for anastrozole or exemestane. Under these conditions, letrozole is reimbursed for 3 years in Belgium. If women are postmenopausal at diagnosis and already used an oral AI at any time during the first 5 years, we discuss an extra 5 years of tamoxifen. Results from ongoing clinical trials will tell us whether in these cases prolonged AI use is better than tamoxifen so that therapy can be adapted. Benefit from extended adjuvant endocrine therapy is likely larger with better compliance and potential side effects of extended endocrine therapy need to be discussed. Therefore, when advising extended adjuvant endocrine treatment, a balance should always be made between relapse risk and treatment tolerance/compliance.