Changes in adjuvant endocrine therapy over one year among postmenopausal women with early-stage breast cancer initiating aromatase inhibitors.

11 Background: Aromatase inhibitors (AIs) are standard of care for adjuvant endocrine therapy (AET) to prevent recurrence of early stage breast cancer in postmenopausal women. Previous AET adherence research has focused on the 25-96% adherence observed with, but more information is needed about AI adherence, especially regarding the role of arthralgia (joint pain or stiffness) in AET changes. Our objective was to understand AET changes within a year of AI initiation. Methods: We examined AET switching (either to another AI or to tamoxifen), overall changes in AET (including switching and temporary or permanent discontinuation), and physician- and patient-reported arthralgia, using data abstracted from medical records and self-administered surveys among 93 patients initiating AI. We conducted Chi-square and Wilcoxon univariate analyses. Results: Anastrazole was initially prescribed to 64 patients (69%), letrozole to 28 patients (30%), and exemestane to 1 patient. A year after AI initiation, 64 patients (69%) had no change in AET. Among the 29 patients (31%) who had an AET change, 14 switched to at least one other AI, 11 switched to tamoxifen, 9 temporarily discontinued AET, and 7 entirely discontinued AET (categories not mutually exclusive). Average time to first AET switch was 182.7 days. Average number of AET switches was 1.4. Arthralgia was the most common reason for AET changes, noted in the records of 19 patients (66% of those who changed AET). Patients who changed AET reported more severe arthralgia (median pain from 0-10 among 8 joint groups =1.4, interquartile range [IQR]=0.3-2.6) at week 12 than those who did not (median=0.3, IQR=0-1.1), p=0.03. A higher proportion (46%) of the 28 patients who initiated with letrozole changed AET due to arthralgia, compared with 20% of the 64 patients who initiated with anastrazole (p=0.01). Conclusions: A substantial proportion of women initiating AI change AET over one year. Arthralgia appears to play a key role in AET changes, particularly for letrozole as compared with anastrazole. More longitudinal patient-reported arthralgia data are needed to guide clinical decision making about AI initiation and AET changes.