Sentinel lymph node mapping of the colon and stomach using lymphoseek in a pig model

Lymphoseek is a radiopharmaceutical designed for sentinel lymph node (SLN) mapping. The purpose of this study was to compare Lymphoseek colon and gastric pharmacokinetics with filtered [(99m)Tc]sulfur colloid (fTcSC). Eight anesthetized pigs received an endoscopic injection of Lymphoseek or fTcSC in the stomach and colon. Scintigraphy was obtained of both administration sites at 15-minute intervals up to 3 hours after injection, after which all SLNs were identified by a handheld gamma probe through a laparotomy incision. Isosulfan blue was administered at the injection site 5 minutes before SLN mapping. The percentage of injected dose (%ID) was measured for all harvested nodes, and the clearance half-life (T(c)) was calculated for all injection sites. The mean Lymphoseek clearance for colon (T(c), 2.56 +/- 1.04 hours) and gastric (T(c), 3.83 +/- 1.18 hours) injection sites was statistically faster (P =.030) compared with fTcSC (colon T(c), 14.98 +/- 3.41 hours; stomach T(c), 14.52 +/- 4.08 hours). After 3 hours, Lymphoseek exhibited a mean SLN %ID of 1.32% +/- 1.71% in the colon and 2.04% +/- 2.12% in the stomach; this was not statistically different from fTcSC (colon,.63% +/-.39%; stomach, 2.35% +/- 2.90%). SLN uptake of Lymphoseek was significantly different from second-echelon node %ID for the colon (P =.011) and gastric (P =.029) injection sites. All SLNs exceeded 10 times background, and there was no discordance between isosulfan blue and Lymphoseek or fTcSC. Three hours after colon stomach administration, Lymphoseek demonstrated rapid injection site clearance, detectable SLN uptake, and low second-echelon node uptake.