Tumor long-axis diameter and SUVmax predict long-term responders in 90Y-ibritumomab tiuxetan monotherapy

90Y-ibritumomab tiuxetan (90Y-IT) is widely used, but the factors responsible for its optimal treatment effects are unknown. We enrolled 34 patients with relapsed indolent lymphoma treated with 90Y-IT monotherapy at Gunma University Hospital between 2003 and 2014 in the present study. Clinical data including computed tomography and 18-Fluoro-deoxyglucose positron emission tomography were retrospectively analyzed. The overall response rate and complete response rate were 91% and 82%, respectively. The median progression-free survival (PFS) and overall survival were 32 months and not reached, respectively. In univariate analysis, tumor long-axis diameter ≤ 2.5 cm, maximum standardized uptake value (SUVmax) ≤ 6.5, localized disease, normal levels of serum soluble interleukin-2 receptor, and the number of involved nodal sites ≤ 3 immediately prior to 90Y-IT were associated with median PFS greater than 6 years. However, in multivariate analysis, only tumor long-axis diameter ≤ 2.5 cm and SUVmax ≤ 6.5 affected PFS [hazard ratio (HR) 0.130, P = 0.0021 and HR 0.283, P = 0.0311, respectively]. Patients with only one prior regimen needed less granulocyte colony-stimulating factor and platelet transfusion. Thus, 90Y-IT treatment should be considered for patients with indolent lymphoma in first relapse who have tumor long-axis diameter ≤ 2.5 cm and SUVmax ≤ 6.5.