Conference Coverage

Radioligand is highly active in metastatic castrate-resistant prostate cancer


 

REPORTING FROM GUCS 2019

Men with metastatic castrate-resistant prostate cancer (mCRPC) who have exhausted conventional treatment options have very good outcomes when treated with the novel targeted radioligand lutetium-177 PSMA-617 (LuPSMA), finds a single-center phase 2 trial to be reported at the 2019 Genitourinary Cancers Symposium sponsored by the American Society of Clinical Oncology, ASTRO, and the Society of Urologic Oncology.

“Whilst there have been major advances in the last few years with several drugs that prolong survival in these men, the disease remains fatal in a relatively short period of time, and there is an urgent need for new effective therapies,” said lead study author Michael Hofman, MBBS, professor of nuclear medicine at the Peter MacCallum Cancer Centre, Melbourne.

LuPSMA is a radiolabeled small molecule that binds with high affinity to PSMA (prostate-specific membrane antigen), enabling targeted delivery of beta radiation to lesions throughout the body. To be eligible for the trial, patients had to have PSMA-positive disease. Results among the first 30 patients treated showed good activity and acceptable toxicity (Lancet Oncol. 2018;19:825-33), leading to enrollment of an expansion cohort of 20 patients.

With a median follow-up of 23.5 months among all 50 patients, nearly two-thirds achieved a 50% or greater reduction in their PSA level, Dr. Hofman reported in a presscast held before the symposium. Median overall survival exceeded 12 months for the whole cohort and was especially good for the subset achieving that level of PSA reduction, at 18 months.

“This is a single-arm study with no control arm. So whilst my impression is that this is a life-prolonging therapy, this is not a claim that we can make yet because there is no comparator arm with an existing treatment or therapy,” he acknowledged. However, data from the literature suggest that in the absence of this novel radioligand, the patients would likely have survived only about 6-9 months.

“These results in 50 men provide further confidence to our previously published 30-patient cohort, demonstrating high response rates and low toxicity in men with mCRPC who have progressed after multiple conventional therapies,” Dr. Hofman said. The findings also “support a novel mechanism of action for this therapy compared to existing therapies.”

The favorable data have led to initiation of two randomized controlled trials: the phase 2 TheraP trial (NCT03392428) comparing LuPSMA with cabazitaxel (Jevtana), and the phase 3 VISION trial (NCT03511664), comparing LuPSMA with best standard of care. “We really need the larger trials ... to get a confident assessment on whether it improves survival and by how much,” he maintained. “But my impression, seeing these patients come into the clinic very sick and seeing them improve on the therapy, and knowing those averages [for survival without this therapy], is that these trials are likely to be positive.”

“As a clinician, I will tell you that this is a very intriguing agent, and the VISION study, which is a registration trial, is open in the U.S.,” said ASCO expert and presscast moderator Robert Dreicer, MD, MS, MACP, FASCO, deputy director and associate director of clinical research at the University of Virginia Cancer Center and professor of medicine and urology at the University of Virginia, Charlottesville.

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