New PET Agent Aims to Find Prostate Cancer Metastases Earlier
The early clinical trial of a PET radiotracer called zirconium-89 (Zr-89) Df-IAB2M (IAB2M) may identify prostate metastases sooner, according to researchers from Memorial Sloan Kettering Cancer Center.

"To date, conventional imaging is limited in detecting prostate cancer metastasis accurately and measurably," says Neeta Pandit-Taskar, MD, coauthor of the study and a researcher at Memorial Sloan Kettering Cancer Center in New York. "Using this agent, we can detect the prostate cancer cells that have metastasized to bone—one of the most difficult areas to evaluate using standard methods. We hope this research will help us develop earlier and more effective detection of disease and assist in clinical decision-making."

The radiotracer combines a small amount of the radioactive material Zr-89 with a fragment of an antibody called a minibody. This minibody has anti-prostate-specific membrane antigen (PSMA) qualities and attaches to overexpression of the enzyme on the exterior of prostate cancer cells wherever they may have traveled in the body. The IAB2M is imaged faster than the full antibody that targets PSMA and has been shown to be safe for patients.

"Initial results of full-body imaging with this Zr-89 radiolabeled minibody have shown that we are able to detect more disease sites in patients than with conventional imaging," Pandit-Taskar says. "With further validation, this radiotracer could also potentially be used to perform targeted biopsies for precise tissue analysis, which could lead to earlier, more appropriate treatment for prostate cancer patients."

For this research, 28 subjects were imaged with a variety of imaging modalities, including CT, MRI, molecular bone scan (SI), FDG-PET, and PET/CT with IAB2M assessed in escalated doses. A selection of suspected disease sites were then biopsied.

The results showed that there were a total of 393 suspected lesions found in soft tissue and bone using all imaging modalities, collectively. IAB2M PET/CT identified 81.7% of all suspected bone lesions, and 65 of these growths that were not identified with any other modalities. Additionally, IAB2M found 32 soft-tissue lesions not found by other methods.

Of the total 19 biopsies and histological analyses performed, FDG-PET identified 14 growths, IAB2M PET/CT identified 17 growths, and SI found 18. However, overall accuracy of positive/negative reading was found to be 89.5% for IAB2M PET/CT vs 84% for both SI and FDG-PET.

"This is an early phase trial," Pandit-Taskar says. "For the next few years, we will be exploring IAB2M in additional clinical trials. More data are needed to understand its clinical value but, if results are favorable, this imaging agent could play a critical role in the standard of care for prostate cancer."