Stannous colloid mixed with indocyanine green as a tracer for sentinel lymph node navigation surgery

The combined use of a vital dye and radioactive colloid reportedly performs better in detecting sentinel lymph nodes (SLNs) for cancers than the use of either of them alone. However, especially for gastric cancer, two endoscopic procedures are required to administer these two tracers, which burdens the patients and practitioners. Here we propose the use of stannous colloid (SnC) mixed with indocyanine green (ICG) as a new mixed tracer (SnC-ICG); its characteristics were investigated in vivo and in vitro to estimate its usefulness for SLN navigation. The tracers were administered to rats and the accumulation of radioactivity and/or near-infrared fluorescence were evaluated in the regional lymph nodes (LNs) using single positron emission computed tomography and near-infrared fluorescence imaging, respectively. SnC-ICG showed significantly better clearance from the injection site and better migration to primary LNs than the single administration of SnC or ICG aqueous solution. SnC-ICG demonstrated a wide particle size variability, stabilized to 1200-nm upon the addition of albumin in vitro; These properties could contribute to its behavior in vivo. The use of SnC-ICG could contribute better performance to detect SLNs for gastric cancer with less burden on both patients and medical practitioners.