Abstract Background Decision-making regarding antithrombotic therapy (ATT) for patients with advanced cancer is highly challenging, given the competing risks and benefits of this treatment near the end of life. SERENITY is a Pan-European study aiming to develop and evaluate a shared decision-making support tool (SDMST), to facilitate ATT management with patients with advanced cancer, at the end of life (1). Purpose To explore patients’ and clinicians’ views, perspectives and experiences of ATT treatment and decision making. These data will form part of the evidence base to develop and evaluate a SDMST to support decision-making with patients with advanced cancer receiving ATT. Methods Semi-structured interviews were conducted with patients and clinicians involved in ATT treatment and management in the UK, Denmark, France and Spain. Data were analysed using Framework Analysis; the thematic framework was informed by concomitant SERENITY work packages, interview transcripts/summaries and patient and public representatives. Results Fifty-nine patients and 77 clinicians were interviewed across the four countries. Some patients expressed a preference not to be involved or informed, while others felt they should have the ultimate authority over ATT prescribing decisions. For many, there was little distinction between being informed about the decision and being involved in the decision regarding ATT; ultimately, many patients expressed the doctor should make the final decision. However, many patients did not perceive there to be a decision to make, either due to the complexities of the choice to be made, or that there are circumstances in which they should discontinue ATT. Similarly, while patients relied heavily on the doctors’ expertise, clinicians described significant reliance upon the patient perspective, due to the complexity of competing risks and benefits, and the context of advanced cancer/multi-comorbidities. Some patients reported being highly concerned about the risks of ATT deprescription, while others did not have a strong opinion on this treatment, deferring to their clinicians’ expertise. Thus, a discordance in decision-making perceptions between patients and clinicians was evident. Moreover, the decision is multifaceted in nature; the context of advanced cancer, coupled with the possibility that the clinician prescribing ATT may not serve as the primary clinician during the time when ATT decisions must be made, further complicated both the decision-making process and the opportunity for shared decision making. Conclusion There appears to be discordance in decision-making perceptions between patients and clinicians, which could negatively influence the co-decision making regarding ATT, contributing to prescribing inertia, and potentially impacting patient outcomes. A SDMST may help support the complexity around the decision, ensuring informed choices are made, and patients’ wishes and values are incorporated into the decision.