Real-World Analysis of Olanzapine and Functional Outcomes in Outpatient Cancer Rehabilitation

Background/Objectives: Cachexia is a multifactorial muscle wasting syndrome driven by inflammation, causing increased catabolism and decreased food intake. Using appetite stimulation as part of multidisciplinary rehabilitation for cachexia is an emerging strategy. Olanzapine was originally developed as an atypical antipsychotic and has since emerged in rehabilitative strategies in patients with brain injury and chemotherapy-induced nausea. In 2023, the American Society of Clinical Oncology (ASCO) issued a rapid recommendation for the use of low-dose (2.5–5 mg) olanzapine to improve appetite and weight in adults with advanced cancer cachexia, based on novel evidence of increased appetite and weight gain. Methods: We retrospectively evaluated the impact of olanzapine on a real-world cohort of 45 patients with appetite concerns undergoing cancer-related rehabilitation. Patients were retrospectively evaluated for changes in body composition metrics and physical therapy (PT) related outcomes. Results: While treatment groups were well matched at baseline, there were no statistical differences between group outcomes, including weight gain, contrary to findings in other populations. However, fatigue was a significant predictor of PT goal completion across the cohort (p = 0.017), highlighting the need for future studies to investigate this relationship more deeply. Conclusions: These results indicate that the effects of olanzapine may vary between different clinical populations and suggest that further investigation into adjuvant therapies remains critical for optimizing care for cancer patients with anorexia.