11504 Background: Management of chemotherapy-induced nausea and vomiting (CINV) remains challenging. OLN might provide several benefits over APR which is current standard of care – particularly in terms of nausea control and cost effectiveness. However, sedation associated with recommended doses of olanzapine precludes its wide use in oncology practice. Methods: This was randomized phase II single center study aimed to compare OLN and APR in CINV prophylaxis. Key inclusion criteria were: chemo- and radio-therapy naïve patients, planned administration of high-emetogenic chemotherapy (cisplatin, carboplatin AUC≥4, doxorubicin etc). Patients were randomized 1:1 ratio in the following arms: olanzapine 5 QD day 0-4 or aprepitant 125 mg day 1, 80 mg day 2,3. All patients received ondansetron 16 mg day 1 and dexamethasone 8 mg day 1-3. Primary endpoint was complete nausea control (no nausea and no rescue medication) 0-120 hours after chemotherapy. Complete response (no emesis and no rescue medication) was a key secondary end point. Nausea was assessed using MASCC Antiemesis Tool. Sample size: 94 patients to increase nausea control rate from 40 to 70% (α = 0.05; β = 0.80; 10% of estimated data loss). Results: We included in the analysis 93 patients who could be evaluated. The groups were well balanced, median age was 49 years, vast majority of patients (95.6%) were females. The proportion of patients with complete nausea control in OLN and APR groups was 44.2% and 24.0% respectively (RR 2.5; 95% CI 1.04-6.08; p = 0.039). Complete response was achieved in 74.4% and 54.0% patients respectively (RR 2.48; 95% CI 1.026-5.99; p = 0.041). No differences in rates of undesired sedations were detected. Conclusions: Our data suggests superiority of OLN regimen in terms of nausea control. This regimen deserves further investigation. Clinical trial information: NCT03478605.