Clin Breast Cancer

Background:Endocrine therapy adherence remains a barrier to optimal estrogen receptor positive (ER+) breast cancer outcomes. We theorized that experience navigating difficult medication regimen factors, such as route of administration complexity, may improve subsequent adherence following stressful cancer diagnoses, but not in patients with bipolar and psychotic disorders at-risk for poor access and non-adherence.Methods:We included 21,894 women aged 68 or older at their first surgically treated stage I-IV ER+ breast cancer (2007-2013) from the SEER-Medicare dataset, 5.8% having bipolar and psychotic disorders. We required continuous fee-for-service Medicare (Parts A and B) for at least 36 months before and 18 after cancer diagnosis. \u201cMedication regimen factors\u201d in the Part D claims four months prior included the number of all medications used, pharmacy visits, and administration complexity (Medication Regimen Complexity Index subscale). Cox regression was used to model time-to-initiation and discontinuation, with longitudinal linear regression for adherence to endocrine therapy.Results:Women with more frequent prior medication use and pharmacy visits were more likely to initiate [\u201c4+ Meds & 2+ Visits\u201d vs \u201cNo Meds\u201d HR 1.47 (95% CI 1.33-1.63)], adhere [+6.0% (95% CI 4.3-7.6)], and continuously use endocrine therapy [discontinuation HR 0.48 (95% CI 0.39-0.59)]. Medication administration complexity had modest effects. Difficult medication regimens were more common among patients with bipolar and psychotic disorders but had no statistically significant effects.Conclusions:Experience with frequent prior medication use and pharmacy visits may increase likelihood of endocrine therapy use in most patients, but not in those with bipolar and psychotic disorders.HHSN261201000140C/CA/NCI NIH HHS/United StatesHHSN261201000035C/CA/NCI NIH HHS/United StatesP30 CA086862/CA/NCI NIH HHS/United StatesHHSN261201000035I/CA/NCI NIH HHS/United StatesHHSN261201000034C/CA/NCI NIH HHS/United StatesT32 GM007337/GM/NIGMS NIH HHS/United StatesU58 DP003862/DP/NCCDPHP CDC HHS/United StatesR01 MD010728/MD/NIMHD NIH HHS/United States2021-06-01T00:00:00Z32139273PMC71035217791vault:3517