Lymphoseek: a molecular radiopharmaceutical for sentinel node detection

Lymphoseek is a new radiopharmaceutical that accumulates in lymphatic tissue by binding to a receptor that resides on the surface of macrophage cells. We conducted a phase I clinical trial in which Lymphoseek was compared with filtered [(99m)Tc]sulfur colloid (fTcSC) for sentinel node detection in patients with breast cancer. Twelve women (42-71 years) with breast cancer were randomly assigned to a 3-hour imaging protocol with peritumoral/subdermal injections (.5 mCi) of either Lymphoseek (1 nmol; molecular weight, 28 kDa; diameter,.007 micro m) or.2 micro m of fTcSC. Serial images were acquired for 180 minutes. Sentinel nodes, excised within 4.2 to 7.3 hours of administration, were assayed in a dose calibrator. The receptor-binding agent, Lymphoseek, exhibited a significantly (P =.0025) faster injection site clearance (rate,.255 +/-.147/hour; fTcSC rate,.014 +/-.018/hour); the mean Lymphoseek clearance half-time was 2.72 +/- 1.57 hours compared with 49.5 +/- 38.5 hours for fTcSC. The primary sentinel node uptake of Lymphoseek (range,.02%-1.12%; mean,.55% +/-.43%) and fTcSC (range,.00%-1.93%; mean,.65% +/-.63%) did not differ (P =.75). Lymphoseek exhibited a lower mean number of sentinel nodes per study (n = 1.3) than fTcSC (n = 1.7) and a higher concordance with Lymphazurin. The molecular receptor-binding agent Lymphoseek demonstrated faster injection site clearance and equivalent primary sentinel node uptake when compared with fTcSC.