Objective: The aim of this study was to investigate the extent of discontinuation of oral adjuvant endocrine therapy (OAET) in women nearly 4 years from the diagnosis of their first episode of invasive breast cancer and the reasons for such discontinuation.
Methods: We used a large, prospective cohort study of women who had been diagnosed with their first episode of invasive breast cancer between 2004 and 2006, recruited through a state-based cancer registry. All participants completed an enrollment questionnaire (EQ) within 12 months of diagnosis and annual follow-up questionnaires (FQs) thereafter. The data in this report were obtained from the EQ and the first three FQs.
Results: A total of 1,370 women with hormone receptor–positive disease completed the EQ. At the completion of the third FQ nearly 4 years from diagnosis, 1,193 women remained in the study. Use of OAET peaked by 2 years postdiagnosis. At nearly 4 years from diagnosis, 18% of the 1,193 women remaining in the study were not taking OAET. Of these women, just more than half had ceased therapy mainly owing to a range of adverse effects, predominantly estrogen deficiency symptoms, but the remainder (8% of women remaining in the study) had never used OAET.
Conclusions: Our study confirms that early discontinuation of OAET due to estrogen deficiency symptoms remains an important issue despite calls for strategies to address this problem. The number of women potentially suitable for OAET but not receiving it was almost as great as the number of those who have discontinued therapy.