Introduction

Breast cancer (BC) is the most prevalent cancer among women globally, representing approximately 30% of female cancer diagnoses [1], with over 2 million new cases annually [2]. Approximately 70% of the patients have hormone receptor-positive (HR+) and human epidermal growth factor receptor-negative (HER2−) BC [3], a subtype associated with better prognosis and favorable initial responses to endocrine therapy (ET) [4]. Despite this, 25–30% eventually develop metastatic disease (MBC) [5].

HR+/HER2− MBC remains incurable and ET is the standard treatment, although resistance is common [1, 6]. To improve outcomes in this setting, oral cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors like abemaciclib have become widely used [6–8]. In MONARCH-2 and -3, abemaciclib plus ET significantly improved progression-free survival but was frequently associated with diarrhea (over 80% of patients) and caused treatment discontinuation in 2–3% [9, 10].

Diarrhea and other adverse events (AEs) can compromise adherence, delay treatment, and lead to dose reductions or discontinuations [11]. The early identification and management of AEs—including education and prompt identification of low-grade toxicities, plus nutritional counseling and supportive care—are key to maintaining adherence and optimizing outcomes [11].

Patient support programs (PSPs) offer strategies to enable patients to manage their disease and associated adverse events. These programs often focus on individualized counseling and fostering effective communication between patients and healthcare professionals (HCPs), aiming to enhance treatment adherence, improve clinical outcomes, elevate the patient experience with treatment, and/or increase their quality of life [12].

In this context, in Spain, patients starting treatment with abemaciclib for MBC can voluntarily participate in a PSP sponsored by the marketing authorization holder. This program offers telephone education 24/7 by nurses in a call center through both outbound and inbound calls, providing guidance on self-care, nutrition, and management of side effects, particularly diarrhea. Nurses provide support, advice, and information, always referring the patient to the treating oncologist for any treatment-related decisions, such as dose changes or interruptions [13].

Despite the increasing availability of PSPs for oncological patients, there is a lack of published evidence on their quantifiable impact, particularly in the management of treatment-related AEs (12). This study aimed to assess the clinical impact of abemaciclib PSP on managing abemaciclib-related diarrhea. The findings may offer valuable insights into the potential benefits of these strategies for patients.