Lymphoseek: A molecular radiopharmaceutical for sentinel node detection

Background: 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 1 clinical trial in which Lymphoseek was compared with filtered [Tc-99m]sulfur colloid (fTcSC) for sentinel node detection in patients with breast cancer. Methods: 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 mum) or .2 mum 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. Results: 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. Conclusions: The molecular receptor-binding agent Lymphoseek demonstrated faster injection site clearance and equivalent primary sentinel node uptake when compared with fTcSC.