LAUSR

Background: Despite the well-established survival benefit associated with adjuvant hormonal treatment, younger women with hormone receptor positive (HR+) breast cancer (BC) are less adherent to endocrine therapy (ET) as prescribed, compared to their older counterparts, and may have unique issues that contribute to ET non-adherence. In an effort to identify factors that can be targeted to improve ET uptake and adherence, we sought to evaluate ET initiation in young women with BC. Methods: As part of a multi-center, prospective cohort enrolling women with newly diagnosed BC at age ≤40 years between 2006-2016, we identified 657 women with HR+, Stage 0-III BC. Participants complete serial surveys that included questions about socio-demographics, fertility concerns, and treatment. Women who did not report taking tamoxifen or an aromatase inhibitor (AI) at least once in the 18 months after diagnosis (dx) were classified as non-initiators. Variables significant at p Results: By 18 months post-dx, 15% (99/657) had not initiated ET; among women with Stage 0 BC, 77% (51/66) had not initiated vs 8% (48/591) with invasive BC (p Conclusion: Most young women with HR+ DCIS do not take adjuvant ET despite the potential benefits (substantially reduced risk of local recurrence and contralateral BC) and very low risk of serious toxicity. Among young women with invasive HR+ BC, a significant minority fails to start ET within 18 months of dx. Adjuvant ET non-initiation may contribute in part to the racial and SES outcomes disparities that have been observed. Further study is needed to elucidate barriers to initiation with the goal of developing targeted interventions that will enhance ET initiation and adherence in general. Citation Format: Rosenberg SM, Gelber S, Ruddy KJ, Tamimi RM, Schapira L, Borges VF, Come S, Meyer ME, Partridge AH. Drugs don9t work if people don9t take them: Non-initiation of endocrine therapy in young women [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-09-07.