Ingrid Hein

December 04, 2017

Emerging agents for prostate imaging will dramatically improve the ability to determine the location of cancerous legions, which will, in turn, allow the precise targeting of radiotherapy, new research shows.

"This is an exciting time in radiology," said Frederik Giesel, MD, Universität Heidelberg in Germany.

One agent — 18F-PSMA-1007 — has some characteristics that are different from other agents, he explained to audiences during his presentation of three different studies at the Radiological Society of North America 2017 Annual Meeting in Chicago.

"It has a longer shelf life than the others and minimal kidney clearance, meaning that urinary excretion of it is minimal," he said. "18F-PSMA-1007 is the first tracer that has a different elimination route, which I would say is an advantage."

But more important is the increased uptake in tumor tissue, he told Medscape Medical News. Its tumor-to-background ratio makes the detection of small lymph node metastases easier than with other agents.

"We see advantages of diagnostic performance in this tracer," he added.

In a study published earlier this year, Dr Giesel and his colleagues demonstrated that 18F-PSMA-1007 has a 95% sensitivity for small lymph node metastases (Eur J Nucl Med Mol Imaging. 2017;44:678-688).

In a new study, Dr Giesel's team looked at the diagnostic potential of 18F-PSMA-1007. They analyzed biodistribution in the normal organs and tumors of seven patients with a biochemical recurrence of prostate cancer, and assessed lesion size.

Patients were injected with 18F-PSMA-1007 and underwent PET–CT scanning 1 hour and 3 hours after injection.

Local recurrence was detected in two patients with prostate-specific antigen (PSA) levels of 1.9 and 3.6 ng/mL, lymph node metastases was detected in two patients with PSA levels of 0.16 and 2.0 ng/mL, and bone metastases was detected in one patient with a PSA level of 3.8 ng/mL. In the other two patients, with PSA levels of 0.4 and 0.5 ng/mL, PET-positive findings were not observed.

Tracer uptake increased in all tumor lesions from 1 hour postinjection to 3 hours postinjection (increase in mean maximum standardized uptake value [SUVmax], 8.4 to 14.1).

The 18F-PSMA-1007 tracer had high potential for noninvasive localization diagnostics in prostate cancer patients with recurrence, the researchers conclude. And low urine activity in the bladder and urethra are advantages for this tracer.

Emerging Agents

"Everyone is excited. We are now able to identify prostate cancer early and accurately," said Andrei Iagaru, MD, from the Stanford University School of Medicine in California.

These new radiopharmaceuticals will play important roles at all stages of prostate cancer.

"These new radiopharmaceuticals will play important roles at all stages of prostate cancer," he told Medscape Medical News.

During his presentation, Dr Iagaru highlighted the performance of these new classes of diagnostic and therapeutic agents by describing his experience with 68Ga-PSMA-11 and gastrin-releasing peptide receptor (GRPR) ligands for the imaging of prostate cancer at initial diagnosis and biochemical recurrence.

Until now, patients with elevated PSA levels and suspected prostate cancer have received "blind prostate biopsies," he explained. But with the new agents, receptors overexpressed on the surface of prostate cancer cells are identified, allowing for targeted biopsies.

At the more advanced stages of disease, "they can then be labeled to take a picture," said Dr Iagaru. "And once we see exactly where the cancer cells are and have a key locked in on the target, we can kill them with a different type of radioactive material attached to the same core."

68Ga-PSMA-11 can be used to successfully image prostate cancer, but it has "a short half-life and production limitations," said Dr Giesel.

His group selected 18F-PSMA-1007 because of its demonstrated high labeling yields, outstanding tumor uptake, and fast nonurinary background clearance, which minimizes radiation exposure to other parts of the body. "This agent is much more precise, compared with others, for N and M staging, and opens a new field of radiology, where we also consider PET for an important part of patient stratification."

Dr Giesel has a patent application for 18F-PSMA-1007. Dr Iagaru has received a research grant from General Electric Company.

Radiological Society of North America (RSNA) 2017 Annual Meeting: Abstracts SSA16-06 (Giesel) and SSA16-07 (Giesel), presented November 26, 2017; abstracts SPSH52D (Giesel) and SPSH52B (Iagaru), presented November 30, 2017.

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