Development of 125I-methylene blue for sentinel lymph node biopsy

Background Sentinel lymph node biopsy is an established alternative to complete lymph node dissection in some patients. We have developed a novel, radiolabeled methylene blue dye that may be a useful alternative to the traditional two-step procedure involving 99mTc–labeled colloid and unlabeled blue dye. We hypothesize that 125I-labeled methylene blue will be rapidly absorbed into the lymphatics and transported to the drainage basin containing the sentinel nodes. Materials and Methods Rabbits footpads were injected with 1 mCi of 125I-labeled methylene blue admixed with unlabeled dye. A hand-held gamma detection device allowed tracking of radiolabeled dye to nodes in the popliteal and inguinal regions. At pre-established time points animals were sacrificed, and the nodal basin dissected. Nodal radioactivity as well as uptake of blue dye was recorded. Results The spread of the radiolabeled methylene blue compound from the footpad to the popliteal lymph nodes occurred in 5–10 min. Conclusion The radiolabeled dye rapidly progresses through lymphatics to the draining nodes. Use of radiolabeled methylene blue may be an attractive alternative to current two-step sentinel node techniques, as it may be less painful, and may reduce the cost associated with the time-delay between the injection of the radioactive compound and surgery. J. Surg. Oncol. 2006;94:293–297. © 2006 Wiley-Liss, Inc.