Background: Biodistribution data to date using In-ibritumomab tiuxetan have been initially obtained in patients with less than 25% lymphomatous bone marrow involvement and adequate hematopoietic synthetic function. In this article we present the results of an analysis of the biodistribution data obtained from a cohort of patients with extensive bone marrow involvement, baseline cytopenias, and chronic lymphocytic leukemia (CLL).
Materials and methods: Thirty-nine patients with a diagnosis of B-cell lymphoma or CLL expressing the CD20 antigen, who had failed at least one prior regimen, and had evidence of persistent disease were included in this analysis; however, only 38 of them completed the treatment. Semiquantitative analysis of the biodistribution was performed using regions of interest over the liver, lungs, kidneys, spleen, and sacrum. The observed interpatient variability including higher liver uptake in four patients is discussed.
Results: No severe solid organ toxicity was observed at the maximum administered activity of 1184 MBq (32 mCi) Y-ibritumomab tiuxetan. After accounting for differences in marrow involvement, patients with CLL exhibit comparable biodistributions to those with B-NHL. We found that the estimated sacral marrow uptake on 48 h images in patients with bone marrow involvement may be an indicator of bone marrow involvement. There was no correlation between tumor visualization and response to treatment.
Conclusion: These data suggest that the imaging step is not critical when the administered activity is below 1184 MBq (32 mCi). However, our analysis confirms that the semiquantitative imaging data can be used to identify patients at risk for liver toxicity when higher doses of Y-ibritumomab tiuxetan are used. Patients with CLL can have excellent targeting of disease by In-ibritumomab tiuxetan, indicating potential efficacy in this patient population.