A new agent, blue and radioactive, for sentinel node detection

Background: Although with some disadvantages, combining radiotracer and isosulfan blue facilitates the detection of sentinel lymph nodes. This study was designed to evaluate the use of Tc-99m-labeled phthalocyanine tetrasulfonate (Tc-99m-PCTS) as a single agent for simultaneous blue staining and radiotracer localization of the sentinel lymph node. Methods: Twelve rabbits were injected into the dermis and subcutaneously in the distal hind limb with 1 mL of blue Tc-99m-PCTS (.5 mCi). The popliteal and inguinal fossae were explored between 15 minutes and 24 hours after injection for blue and/or radioactive tissue. Popliteal and inguinal fossae and other lymph nodes and organs were harvested for determination of the concentration of radioactivity and for histology. Results: Within minutes of Tc-99m-PCTS injection, the lymphatic channels were easily identified by the blue color. At 10 minutes, the radioactive count over the popliteal fossa was significantly higher than over other areas. At exploration, a blue and radioactive popliteal node was identified in all animals; inguinal nodes were neither blue nor radioactive. At death, the radioactivity in the popliteal node was 1000 times higher than in other nodes or organs. Although fainter, the blue color in the popliteal node was still visible at 6 weeks. Histological sections of popliteal node identified the dye in the cytoplasmic compartment of the cells. Conclusions: Technetium-99m PCTS is a single agent that identifies sentinel lymph nodes by color and radioactivity and is retained for an extended period of time without migrating to other tissues.