Patterns of use of oral adjuvant endocrine therapy in Australian breast cancer survivors 5 years from diagnosis

Objective: Oral adjuvant endocrine therapy (OAET) substantially improves the survival of women with hormone receptor-positive (HR+) breast cancer. However, we reported previously that at 3 to 4 years after diagnosis, 18% of affected women are not using OAET primarily because of estrogen deficiency symptoms. The aim of this study was to determine the use of OAET in women with HR+ breast cancer 5 to 6 years from diagnosis. Methods: Analysis was carried out using data from the Bupa Health Foundation's Health and Wellbeing After Breast Cancer Study, a cohort study of 1,683 women with breast cancer who were recruited in Victoria, Australia between 2004 and 2006. All women completed an enrollment questionnaire within 12 months of diagnosis and an annual follow-up questionnaire (FQ) for 5 years. The fifth FQ was completed 5.7 years from the time of diagnosis. Use of OAET was self-reported in response to a series of questions. Results: A minimal exposure to OAET of at least 5 years (OAET in all six FQs) was reported by 19.7% of the women (n = 212), and another 46.7% (n = 503) received a minimal exposure of at least 4 years (OAET in five questionnaires). In total, 82.1% (n = 883) of the women would have received at least 3 years of treatment (OAET in at least four questionnaires). Only 7.8% (n = 84) reported never using OAET. Conclusions: Most women with HR+ breast cancer who survive at least 5 years have persisted with OAET despite the adverse effects of estrogen depletion.