Applying PET to broaden the diagnostic utility of the clinically validated CA19.9 serum biomarker for oncology

Despite their considerable advantages, many circulating biomarkers have well-documented limitations. One prominent shortcoming in oncology is a high frequency of false-positive indications for malignant disease in upfront diagnosis. Because one common cause of false positivism is biomarker production from benign disorders in unrelated host tissues, we hypothesized that probing the sites of biomarker secretion with an imaging tool could be a broadly useful strategy to deconvolute the meaning of foreboding but inconclusive circulating biomarker levels. Methods: In preparation to address this hypothesis clinically, we developed ⁸⁹Zr-5B1, a fully human, antibodybased radiotracer targeting tumor-associated CA19.9 in the preclinical setting. Results: ⁸⁹Zr-5B1 localized to multiple tumor models representing diseases with undetectable and supraphysiologic serum CA19.9 levels. Among these, ⁸⁹Zr-5B1 detected orthotopic models of pancreatic ductal adenocarcinoma, an elusive cancer for which the serum assay is measured in humans but with limited specificity in part because of the frequency of CA19.9 secretion from benign hepatic pathologies. Conclusion: In this report, a general strategy to supplement some of the shortcomings of otherwise highly useful circulating biomarkers with immunoPET is described. To expedite the clinical validation of this model, a human monoclonal antibody to CA19.9 (a highly visible but partially flawed serum biomarker for several cancers) was radiolabeled and evaluated, and the compelling preclinical evidence suggests that the radiotracer may enhance the fidelity of diagnosis and staging of pancreatic ductal adenocarcinoma, a notoriously occult cancer.