LAUSR

e16546 Background: Radium-223 (Xofigo) has been shown to increase overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) via the phase 3 ALSYMPCA study. The side effect of persistent pancytopenia was noted in 2% of the patients, however, the incidence seen in our institutional clinical practice is higher than reported in the literature. This analysis serves to identify predictive factors and thereby help impact future therapy directions in this patient population. Methods: A retrospective analysis was performed analyzing patients with mCRPC who received xofigo at UFHealth in a 3 year span (from January 2014 to January 2017). Data collected included CBC, ECOG functional status, kidney and liver function, evidence of bony disease on imaging, prior chemotherapy regimens, total radiation dose, and PSA. This study was IRB approved. Results: 52 patients with mCRPC were identified, 27 of which received xofigo. 23 patients received treatment at UF, and one was lost to follow-up. 16 patients (73%) completed the full course (6 doses) of xofigo, while 6 did not. 10 patients (45%) developed pancytopenia, with 2 recovering counts within eight months while the other 8 had persistent cytopenias (6 of which were transfusion-dependent). Older age (74.0 ± 8.8 vs 68.7 ± 10.2) and higher ECOG score (1.6 ± 0.7 vs 1.2 ± 0.6) correlated with increased risk of pancytopenia. In addition, a higher percentage of patients who received prior radiation therapy were more likely to develop pancytopenia (90% vs 75%). All patients studied had bony disease and received prior chemotherapy. Conclusions: Albeit with a limited sample size, we found a higher rate of xofigo-induced pancytopenia in our patient population than the 2% reported in the literature. This may influence clinical decision making in the treatment of mCRPC, as pancytopenia may preclude patients from other survival-prolonging therapies. Factors such as age, functional status, and prior radiation therapy are important to keep under consideration prior to xofigo treatment. Additional larger studies are necessary to further quantify this effect.