Factors Associated with the Decision to Continue Adjuvant Endocrine Therapy for Five More Years in a Diverse Sample of Breast Cancer Survivors.

319 Background: Guidelines suggest that breast cancer survivors consider taking adjuvant endocrine therapy for 10 years post diagnosis to maximize recurrence prevention. Little is known about how patients decide to continue endocrine therapy beyond 5 years. Methods: iCanCare is a longitudinal study of women diagnosed with breast cancer in 2014-15 and reported to the Los Angeles County and Georgia Surveillance, Epidemiology and End Results (SEER) registries. Women were surveyed during initial treatment and again 6 years later (2021-22) (Expected final N=1430, 60% current response rate). The proportion of respondents who completed 5 years of endocrine therapy was determined from SEER and patient report (N=793). This group was queried regarding their decision to continue for an additional 5 years (yes/no/undecided). Patients were asked about the importance of personal values in making this decision (all categorized into very/quite/somewhat important vs. a little/not important), and perceived benefit of continuing (none, small/moderate, large/huge). They were also asked to report on how the decision was made (decision style, involvement of oncologist and primary care physician, PCP). We conducted bivariate analyses to assess associations between the decision to continue (yes vs. no/undecided) and decision-making factors. Results: In the sample of 793 women who completed 5 years of endocrine therapy, 40% decided to take it for more than 5 years, 54% decided not to, and 5% were undecided. Overall, 44% reported that it was a shared decision between them and their physician(s). The values survivors reported as most important in their decision to continue were doing what their oncologist wanted them to do (77%) and worry about recurrence (61%). Medication costs (11%) was the least important factor. Among survivors who chose to continue, most important were doing what their oncologist wanted them to do, worry about recurrence, and desiring the most extensive treatment possible (all p <0.001). A greater proportion of those who perceived a large/huge benefit (vs. less benefit) of continued therapy chose to continue (87% vs. 13%, P<0.001). Having received a strong oncologist recommendation was strongly associated with the decision to continue, as was PCP involvement in the decision (both p<0.001). Conclusions: In this population-based sample of breast cancer survivors who completed 5 years of adjuvant endocrine therapy, less than half decided to extend therapy for 5 more years. Personal values and role of physicians weighed heavily into the decision to continue. Further work to understand how to incorporate and address patient values in endocrine therapy decision making is needed.