BY THE OPTIMIST DAILY EDITORIAL TEAM
Immunotherapy has reshaped cancer treatment over the past decade. It has worked for melanoma, lung cancer, and several other tumor types. Prostate cancer, though, has largely been left out. Researchers classify it as “immune-cold,” meaning the body’s immune system doesn’t recognize or attack it effectively, making it resistant to the class of treatments that have changed outcomes elsewhere. A new drug called VIR-5500 may be changing that picture.
In an early-stage clinical trial, 58 men with advanced prostate cancer who had stopped responding to existing treatments were given VIR-5500, an engineered antibody developed by Vir Biotechnology. The results were presented at the American Society of Clinical Oncology genitourinary cancers symposium in San Francisco and have not yet been peer-reviewed, but they caught the attention of researchers well beyond the team that ran the study.
What the numbers show
At the highest dose tested, 82 percent of patients saw their PSA levels drop by at least half. PSA, or prostate-specific antigen, is a protein whose levels in the blood are used to track disease activity. Of those same patients, 53 percent saw PSA drop by at least 90 percent, and 29 percent by at least 99 percent.
Of 11 patients at the highest dose whose tumors were measurable, five showed tumor shrinkage. One case stood out in particular: a 63-year-old man whose cancer had spread to his liver had 14 cancerous liver lesions that “completely resolved” after six cycles of treatment. The majority of participants, 88 percent, experienced only mild side effects.
“We do need more data but the results are stunning,” said Prof. Johann de Bono of the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust, who led the research. “We believe that such treatments may in the long term lead to cures.”
How VIR-5500 works
VIR-5500 is a T-cell engager, a type of drug that introduces the immune system’s killer T-cells to tumor cells that are trying to evade them, allowing the T-cells to destroy them. Other drugs in this class have triggered severe inflammatory responses in prostate cancer patients, which has limited their use.
What makes VIR-5500 different is that it’s designed to activate only inside the tumor. This keeps side effects low and also allows the drug to stay in the bloodstream longer, which could mean fewer doses needed over time.
What researchers are saying
Charlotte Bevan, professor of cancer biology at Imperial College London, who was not involved in the research, called the potential advance “very exciting,” noting it opens up a new class of drug for prostate cancer. She also flagged something worth watching as trials expand: ensuring diverse patient populations are included, given known disparities in prostate cancer outcomes across ethnicities.
Simon Grieveson, assistant director of research at Prostate Cancer UK, put the stakes plainly. “With over 12,000 men dying from prostate cancer each year in the UK, we urgently need new and innovative ways to treat the disease,” he said. “These early results are extremely promising, with a number of men on the study responding positively to the treatment with minimal side effects. I look forward to seeing this now tested in larger trials, with the hope that this treatment will offer men more valuable time with their loved ones.”
De Bono confirmed that further clinical trials are now being planned. These are early results, not yet peer-reviewed, and phase one trials don’t always hold up at larger scale. But for a cancer type that has resisted immunotherapy for as long as prostate cancer has, seeing tumors shrink and lesions resolve is the kind of signal that makes the next trial worth doing.
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