title: Quantitative comparison of direct antibody labeling and tumor pretargeting in uveal melanoma.
abstract: SPECT radioimmunoscintigraphy with 99mTc-labeled anti-melanoma monoclonal antibodies (MAbs) 225.28S is being used to detect uveal melanoma. Recently, pretargeting methods have been described to reduce background activity and perform imaging in a shorter time interval.
  
  
  METHODS
  We compared the three-step pretargeting method with conventional radioimmunoscintigraphy in 15 patients with a clinical and laboratory diagnosis of uveal lesion. High-resolution SPECT radioimmunoscintigraphy was performed in all patients with directly labeled MAbs and, 1 wk later, with the three-step pretargeting technique. Eleven patients underwent eye enucleation and specimens of uveal melanoma were available for histology, whereas four patients underwent conservative therapy. The percent injected dose (%ID) delivered to the tumor and the tumor-to-background ratio were calculated.
  
  
  RESULTS
  In all three-step radioimmunoscintigraphy studies, there was a reduction of nonspecific nasopharyngeal background. The three-step radioimmunoscintigraphy tumor-to-nontumor ratio was 3.1 +/- 1.3 versus 1.5 +/- 0.5 of conventional radioimmunoscintigraphy, while the percent injected dose on the tumor was similar for the two methods (4.4 +/- 3.0 versus 3.8 +/- 2.8) x 10(-3).
  
  
  CONCLUSIONS
  Improved SPECT imaging with the three-step radioimmunoscintigraphy results from reduced background and from higher counting statistics due to reduction of time interval between radiotracer administration and imaging, whereas the absolute amount of tracer delivered to the tumor by the two methods is comparable.
authors.affiliation: Department of Ophthalmology, University of Milan, Institute H S. Raffaele, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Magnani
authors.forename: G
authors.initials: G
authors.lastname: Paganelli
authors.forename: G
authors.initials: G
authors.lastname: Modorati
authors.forename: F
authors.initials: F
authors.lastname: Zito
authors.forename: C
authors.initials: C
authors.lastname: Songini
authors.forename: F
authors.initials: F
authors.lastname: Sudati
authors.forename: P
authors.initials: P
authors.lastname: Koch
authors.forename: H R
authors.initials: HR
authors.lastname: Maecke
authors.forename: R
authors.initials: R
authors.lastname: Brancato
authors.forename: A G
authors.initials: AG
authors.lastname: Siccardi
authors.forename: F
authors.initials: F
authors.lastname: Fazio
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D001360:Avidin; D001710:Biotin; D002830:Choroid Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D008545:Melanoma / Q000000981:diagnostic imaging* / Q000276:immunology; D016719:Radioimmunodetection / Q000379:methods*; D013667:Technetium; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D000911:Antibodies, Monoclonal; D001360:Avidin; D001710:Biotin; D013667:Technetium