Real-Life Use Patterns of Androgen Receptor Pathway Inhibitors (ARPIs): A Nationwide Register-Based Study in Finland During 2012–2023

<b>Background and Objective:</b> Prostate cancer (PC) is the most common cancer among males in the Western World. Androgens are key growth regulators both in normal and malignant prostate growth. Several new types of androgen pathway inhibitors (ARPIs) have been developed for the treatment of PC. Despite the lack of evidence, sequential use of ARPIs has been adopted into everyday clinical practice. This study aimed to assess real-life ARPI use patterns, especially sequential use and treatment costs, in Finland. <b>Methods:</b> Nationwide register data on all ARPI (enzalutamide, apalutamide, darolutamide, abiraterone) purchases recorded in the National Health Insurance scheme register maintained by the Social Insurance Institution of Finland from January 2012 to December 2023 were used. The data included patient demographics and medicine purchase details, which were descriptively analysed. <b>Results:</b> During the study period, 8369 patients initiated ARPIs. The median age of the users was 75.1 years. Of these, 32.1% (<i>n</i> = 2685) used at least two ARPIs sequentially. The proportion of treatment initiations leading to sequential use increased from 36% in 2012 to 56% in 2017, then decreased to 14% in 2022. The total cost of sequential use was €43.8 million. Limitations include the unrecorded phase of PC. The study's strength is its inclusion of all reimbursed ARPI purchases nationwide. <b>Conclusions</b>: Despite the lack of evidence, sequential ARPI use was initially prevalent but declined after the introduction of new guidelines. Randomised trials are needed to guide the sequential use of these medicines. <b>Patient summar</b><b>y</b><b>:</b> Androgen pathway inhibitors (ARPIs) are widely used in prostate cancer in Finland. One-third of patients use at least two ARPIs sequentially to inhibit testosterone effect. However, there are no large clinical trials published demonstrating the benefits of sequential treatment. More evidence is needed to justify sequential use.