In late March, the FDA approved a new therapy for advanced prostate cancer that is metastasizing, or spreading, in the body. Called Pluvicto (and also lutetium-177-PSMA-617), and delivered by intravenous infusion, the treatment can seek out and destroy tumors that are still too small to see with conventional types of medical imaging.
Pluvicto is approved specifically for men who have already been treated with other anticancer therapies, including chemotherapy and hormonal therapies that block the tumor-promoting hormone testosterone. The drug contains two parts: one that binds to a protein on prostate cancer cell surfaces called PSMA, and a radioactive particle that kills the cancer cells. Most normal cells do not contain PSMA, or do only at very low levels. This allows Pluvicto to attack tumors while sparing healthy tissues.
To confirm whether a man is eligible for the drug, doctors first inject a radioactive tracer that travels the bloodstream looking for and then sticking to PSMA proteins. Cancer cells flagged by the tracer will show up on a specialized scanning technology called positron-emission tomography. About 80% of prostate cancer patients have PSMA-positive tumors; for those who do not, the treatment is ineffective.
During the clinical trial leading to Pluvicto's approval, 831 men were randomly allocated to two groups. One group of men got Pluvicto plus standard-of-care treatments, while men in the control group got standard-of-care only. All the men had metastatic, castration-resistant prostate cancer, meaning that their tumors were spreading and no longer responding to hormonal therapy.
Results and considerations
Results after 21 months showed that Pluvicto was more effective at delaying cancer progression. Among men who got the drug, it took 8.7 months on average for their tumors to start growing again, compared to 3.4 months among men who got standard of care. Pluvicto was also associated with better overall survival: 15.3 months versus 11.3 months. The drug was generally well tolerated, but it also had side effects including fatigue, nausea, kidney problems, and bone marrow suppression.
Dr. David Einstein, a medical oncologist at Beth Israel Deaconess Medical Center in Boston and an assistant professor at Harvard Medical School, describes Pluvicto as a new and exciting tool. Yet he cautioned that while the drug provides a welcome incremental advance for men with advanced prostate cancer, it is not a cure. "Some patients may get the message that Pluvicto replaces all the other available therapies, and this is definitely not the case," he says.
Meanwhile, additional questions remain over who might be able to get the drug. "What about men with metastatic prostate cancer who were never treated with chemotherapy?" Dr. Einstein asks. "If you go strictly by the label, then prior chemotherapy is required. But some men are too sick for chemotherapy, or they may refuse it over potential side effects." Researchers are now conducting studies to determine if Pluvicto is beneficial during earlier stages of prostate cancer, or if combining it with other therapies that might enhance its effects.
"The availability of this new treatment is important for several reasons," said Dr. Marc Garnick, the Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, editor of Harvard Health Publishing's Annual Report on Prostate Diseases, and editor in chief of HarvardProstateKnowledge.org. "First, it extends survival among men who have been heavily treated already and have few therapeutic options remaining. Second, it represents a new approach to using radioactive substances that adds benefit to traditional medicine. And finally, it relies on a diagnostic scan that specifically identifies which men are most likely to benefit from the treatment."