e13054 Background: Combination therapy with cyclin dependent kinase 4 and 6 inhibitors (CDK4/6i: palbociclib, ribociclib and abemaciclib) and endocrine therapy (ET) has markedly improved treatment of hormone receptor positive (HR+), HER2-negative (-) advanced or metastatic breast cancer (MBC) worldwide.However, data is limited on why patients may discontinue CDK4/6i based therapy and how healthcare providers (HCPs) see their role in educating patients (Px) about side effects and supporting compliance. Objective: This study identifies reasons for suboptimal compliance and early discontinuation of CDK4/6i in US HR+ HER2- MBC Px, with a focus on HCPs and Px educational needs related to on-treatment monitoring, side effects and symptom management. Methods: A sequential mixed-methods design was used; 45-minute phone interviews (n=25) informed the development of an online survey (n=193). Both phases included HCPs comprising medical oncologists (ONCs), oncology registered nurses (RNs), nurse practitioners, and physician assistants (NPs/PAs) in community-based settings. Results: Identified areas of improvement for HCPs included: suboptimal competencies were identified: educating Px adequately regarding potential side effects and engaging them to monitor, report, and address them. Among HCPs surveyed, 26%-48% reported suboptimal knowledge of side effects of specific CDK4/6i [Table]. Interviewees noted that educating Px and setting expectations on potential side effects was critical, but 52% of ONCs reported suboptimal skill doing so. A majority of HCPs (68%-91%) expect Px to be able to report all side effects, with half of ONCs considering compliance with medication entirely Pxs’ responsibility, compared with NPs/PAs and RNs at 16-17%. Conclusions: This study identified areas where HCPs can improve their ability to counsel Px and address concerns that may influence a Px’s decision to prematurely discontinue therapy and should be used to inform future professional development initiatives. [Table: see text]