Technetium-99m-labeled rituximab for use as a specific tracer of sentinel lymph node biopsy: a translational research study

PURPOSE: We aimed to develop and translate a CD20-antigen-targeted radiopharmaceutical, Technetium-99 m-labeled ((99m)Tc) rituximab, for sentinel lymph node (SLN) detection. METHODS: (99m)Tc-rituximab was synthesized and tested for stability in human serum. The binding affinity to CD20 was evaluated in Raji cells by flow cytometric analysis. Biodistribution and sentinel node mapping were carried out in bal b/c mice. Eighty-five patients with breast cancer participated in this study. Dynamic sentinel lymphoscintigraphy was first assessed in 12 patients before planar lymphoscintigraphy was assessed in a larger cohort. All patients underwent sentinel lymph node biopsy (SLNB), followed by axillary lymph node dissection. RESULTS: The cell-binding study showed that (99m)Tc-rituximab possessed compatible affinity to human CD20. In the mechanism study, (99m)Tc-labeled anti-mouse CD20 monoclonal antibodies could bind to mouse CD20 and accumulate in the SLN with 2.62±1.25 % of the percentage of injected activity, which could be blocked by excessive unlabeled antibody. Low uptake of non-sentinel nodes and fast clearance from the injection site were observed in the mice. Sentinel nodes were identified in 82 of 85 breast cancer patients (96.5%) by lymphoscintigraphy and SLNB. The sensitivity, specificity, and accuracy were 96.8% (30/31), 100% (51/51), and 98.8% (81/82), respectively. CONCLUSION: (99m)Tc-rituximab, specifically binding to CD20, met most of the requirements of an ideal sentinel mapping agent for use in clinical settings.