Abstract PO3-01-14: Impact of detection mode, tumor characteristics and additional treatment on adherence to adjuvant endocrine therapy after breast cancer in Sweden

Abstract Background: Adjuvant endocrine therapy (AET) reduces recurrence and mortality in women with estrogen receptor (ER) positive early breast cancer (EBC). Adherence to AET has been shown to be lower than expected with risk of worse longtime prognosis. In a nationwide study in Sweden women with breast cancer diagnosis 2008-2010 adherence to AET at 5-year follow-up was estimated at 82,5% which is considered good related to recent published studies (manuscript is under review). Differences between regions and age-groups were shown. Present study investigates the impact on adherence of detection mode, tumor characteristics and additional treatment. Methods: Through the Swedish Cancer Registry (SCR) women with a first primary EBC diagnosed 2008-2010 were identified. From the Swedish National Breast Cancer Registry (NKBC) individual tumor and treatment data were collected. Included in the study was patients with ER positive tumors 10 mm without distant metastasis at diagnosis. Through the Swedish Prescription Registry dispensed treatment from pharmacies was extracted and medication possession rate (MPR) was calculated as number of dispensed doses divided by treatment duration in days. Good adherence to treatment in a patient was set at MPR ≥80%. Adherence at 3- and 5-year follow-up by detection mode, tumor characteristics and additional treatment was estimated. Results: Out of 21 016 women with a first primary BC 2008-2010 registered in the NKBC 10 176 met the inclusion criteria for the study. Among screen-detected tumors the 3- and 5-year adherence were 90,2 respectively 85,1% and 85,4 respectively 78,4% in the non-screen-detected group. In the screen-detected group the tumors were smaller and more often node negative. There was a significantly increased 5-year adherence in patients with stage III disease compared to those with stage I disease (84,1 vs 81,3 %) but not significant at 3-year (89,2 vs 87,3). Adjuvant chemotherapy significantly increased 3- (91.0% vs 85.8%) and 5-year (85.7% vs 79.3%) adherence among screen-detected and non-screen-detected respectively. Conclusions: Adherence to AET in Sweden was good, although there were differences depending on detection mode, tumor stage and additional adjuvant treatment. Stage and additional medical adjuvant treatment depend on each other and should not be seen as independent factors for adherence for AET. Citation Format: Anne Andersson, Anna Von Wachenfeldt, Lennarth Nyström, Frida Isaksson, Pihla Ruohonen. Impact of detection mode, tumor characteristics and additional treatment on adherence to adjuvant endocrine therapy after breast cancer in Sweden abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-01-14.