Metastatic castration-resistant prostate cancer (mCRPC) is among the nastiest variations possible. Death is almost always the end result, and the median survival for men with mCRPC has been less than two years. But a new therapeutic agent – a radioligand – out of Germany has given doctors and patients new hope in their battle with the disease.

Radioligands are radioactive biochemical compounds that may be injected into human tissue, or infused into the bloodstream. The German Society of Nuclear Medicine has recently demonstrated that using lutetium-177 (Lu-177)-labeled PSMA-617 to target prostate-specific membrane antigen may just about even a patient's odds against mCRPC. PSMA is overexpressed in prostate cancer and even more so with castration-resistant disease, so this particular “radioligand therapy” (RLT) seems a tailor-made match.

"Previous studies with a small number of patients have indicated the high potential of this new therapeutic option," explains Kambiz Rahbar, MD, University Hospital Muenster. "This study of a large number of patients at multiple healthcare facilities, however, confirms the efficacy and safety of Lu-177-PSMA-617 radioligand therapy."

At 12 therapy centers across Germany, 145 patients with mCRPC were treated with Lu-177-PSMA-617 between February 2014 and July 2015 with 1 to 4 therapy cycles. A total of 248 therapy cycles were performed in 145 patients. Effectiveness was defined by a prostate-specific antigen decline of 50 percent or more from baseline to at least two weeks after start of RLT. Overall, 45 percent of patients had a positive response following all therapy cycles, while 40 percent responded after a single cycle.

There were a few rough patches, however. Adverse, albeit manageable, side effects noted included: Hematotoxicity occurred in 18 patients: 10 percent experienced anemia; 4 percent, thrombocytopenia (low platelet count); and 3 percent, leukopenia (low white blood cell count). Dry mouth was experienced by 8 percent.

In the final analysis, the study showed that Lu-177-PSMA-617 radioligand therapy is safe and more effective than other third-line systemic therapies for mCRPC patients. The scientists acknowledge that future Phase II and III studies are needed to clarify the survival benefit of this new therapy, which is not yet FDA-approved.

"This therapeutic will provide an additional therapy option for end-stage metastasized, heavily pretreated prostate cancer patients," said Rahbar. "While already demonstrating remarkably high response rates and low toxicity, in the future it may be available at earlier stages of disease with even higher response rates and lower toxicity."

The study is published in the January 2017 issue of the Journal of Nuclear Medicine.