Background: Everolimus, an oral inhibitor of the mammalian target of rapamycin (mTOR), is actually used to prevent organ transplant rejection and treat metastatic breast, renal, and neuroendocrine cancers. Despite significant pharmacokinetic variability among patients, routine therapeutic drug monitoring (TDM) is not commonly used in oncology. Methods: The aim of this multicenter, prospective observational cohort study is to assess the prevalence of everolimus minimum concentration at a steady state (Cminss) falling outside the therapeutic range (10-26.3 ng/mL) during a routine TDM programme. Sixty patients with metastatic breast, neuroendocrine, or renal cancers, either starting or continuing everolimus treatment according to hospital protocols, are to be included between 1st of January 2024 and 31st of December 2025 (patients undergoing clinical trials are excluded). We hypothesize that 30-50% of our patients and their blood samples will not achieve the target optimal plasma concentrations. Blood samples are collected every 4-6 weeks to monitor drug levels. The secondary goal is to explore correlation between out-of-range everolimus levels and factors such as demographic and anthropometric data, treatment specifics, lab results, genetic polymorphisms, and the presence of toxicity. Conclusions: This study could offer valuable insights into optimizing dosing strategies and may contribute to future research on personalizing everolimus and other anticancer treatments. This personalized approach seeks to tailor therapy not only to the tumour's molecular profile but also to the individual characteristics of each patient, improving both drug selection and dosing precision.
Keywords: cancer; everolimus; optimal dosage; pharmacokinetic variability; therapeutic drug monitoring.