Background: Adjuvant endocrine therapy is recommended to extend beyond 5 years for stage II breast cancer, with less consensus for extension in stage I. We aimed to understand use of and decision making about extended endocrine therapy.
Methods: Women aged 20-79 years diagnosed with stage I-II breast cancer in 2014-2015 and reported to Georgia and Los Angeles County Surveillance, Epidemiology, and End Results registries were surveyed at 7 months and again at 6 years postdiagnosis (n = 2361; response rate = 60%). Women with estrogen receptor-positive and/or progesterone receptor-positive disease were asked about their decision whether to continue therapy.
Results: Of 831 women, 591 had completed or were completing 5 years of endocrine therapy. Among those who had decided (n = 557), 46.9% decided to continue (39.4% stage I; 62.4% stage II). On multivariable analysis, factors associated with continuation for stage I were as follows: worry about recurrence (adjusted odds ratio [aOR] = 3.35, 95% confidence interval [CI] = 1.78 to 6.32), desire for most extensive treatment (aOR = 2.15, 95% CI = 1.1 to 4.14), and primary care physician participation (aOR = 4.30, 95% CI = 2.22 to 8.32). Side effects were inversely associated with continuation (stage I: aOR = 0.21, 95% CI = 0.11 to 0.41). Associations were similar for stage II; for stage I only, bilateral mastectomy and chemotherapy were associated with continuation. Decision to continue did not vary by race, ethnicity, or demographic factors.
Conclusions: Nearly 40% of women with stage I breast cancer and two-thirds with stage II decided to extend endocrine therapy. Decision making was influenced by patient values and varied little by stage. These results can inform physician-patient discussion about extending endocrine therapy.
Published by Oxford University Press 2025.