The effects of circulating antigen on the pharmacokinetics and radioimmunoscintigraphic properties of 99m Tc labelled monoclonal antibodies in cancer patients.

UNLABELLED: PURPOSE. This article reports the pharmacokinetics, radiation dosimetry and radioimmunoscintigraphy (RIS) of two (99m)Tc-labelled monoclonal antibodies (MAb) used to detect cancer. METHODS: The effects of circulating antigen in female cancer patients are explored and their effects on the ability of these MAbs to effectively perform as RIS agents noted. To illustrate the effects of circulating antigen, data using MAb B43.13 (OVAREX, AltaRex Corp., Waltham, MA, USA) from a Pilot study in ovarian cancer patients are presented. The results from a Phase II study of MAb 170H.82 (Tru-Scint AD, BIOMIRA INC., Edmonton, Alberta, Canada) in patients with primary and locally recurrent breast cancer were used to portray the biodistribution patterns when no circulating antigen is present. Data from planar gamma camera images were obtained for both groups and used for pharmacokinetic and radiation dosimetry analyses. RESULTS: A pharmacokinetic analysis indicated a shorter residence time and higher clearance of (99m)Tc-MAb-B43.13 that was ascribed in part to the circulating CA 125 antigen in this group of ovarian cancer patients. CONCLUSION: These clearance patterns resulted in acceptable, though higher radiation doses to the spleen and urinary bladder wall for these patients when compared to the MAb-170H.82 group. Both MAbs were found to produce acceptable radioimmunoscintigraphic images