Doctors excited about targeted prostate cancer therapy, but can't prescribe it yet

Dale Cousins was thrilled when he saw his body scans from before and after a new prostate cancer treatment. 

"(The doctor) said, 'Do you see any difference?'" the 79-year-old from Petrolia, Ont., recalled.  

"I said, 'all these spots around my abdomen, they’re gone.'"

Cousins is part of a clinical trial of radioligand therapy, or RLT — a precise targeting of cancer cells with radiation given intravenously. Oncologists say RLT is poised to become a new "pillar" of cancer care, alongside surgery, chemotherapy and radiation. But unlike Cousins, prostate cancer patients who aren't in a clinical trial don't have free access to it.

"We're able to deliver this very specific therapy to specific cells in the body," said Dr. David Laidley, a nuclear oncologist with Western University and London Health Sciences Centre. 

"We're able to deliver lethal radiation therapy specifically targeted to cancer cells and at the same time generally sparing the normal tissues," said Laidley, who is the principal investigator for the London, Ont., site of the Canada-wide clinical trial comparing RLT to chemotherapy. 

Cousins was diagnosed with prostate cancer in 2010 and has been through many treatments, including surgery. After being stable for several years, a scan last year revealed his cancer had spread and he was enrolled in the trial. 

With the last of his six RLT infusions coming on July 10, Cousins has already had a "dramatic reduction" in cancerous lesions and his prostate specific antigen levels have decreased significantly, suggesting an "excellent response," Laidley said.  

Past clinical trials have already shown RLT's effectiveness, leading to Health Canada approving Pluvicto — the radioactive drug that kills the targeted cancer cells — in August 2022 for patients whose prostate cancer has spread and chemotherapy has failed. 

But almost two years later, advanced prostate cancer patients still can't get public access to radioligand therapy because negotiations on how much it should cost government health plans are ongoing. 

While waiting for that decision, there are men with prostate cancer who need the treatment to improve their quality of life and live longer, Laidley said. 

"Oncologists are asking 'can we refer patients or is this an option?' And unfortunately, we have to say that it's not available."

Right now, radioligand therapy for cancer is only publicly available for patients with neuroendocrine tumours, an uncommon but not rare cancer that starts in neuroendocrine cells in the gastrointestinal system or the pancreas, said Dr. Simron Singh, a medical oncologist at Sunnybrook Health Sciences Centre in Toronto.  

Singh was the global principal investigator for a recent international clinical trial that found another radioactive drug delivered through RLT, called Lutathera, reduced neuroendocrine tumour progression and death by 72 per cent when given early after a patient's diagnosis.

Like Pluvicto, Lutathera was already approved in Canada as a last line of cancer treatment but the trial results, published in The Lancet last month, were the first to show that RLT could be used as a "starting treatment," said Singh, who is the co-founder of Sunnybrook's Susan Leslie Clinic for Neuroendocrine Tumours.

In addition to neuroendocrine and prostate cancer, radioligand treatment using different radioactive drugs is currently in clinical trials for other types of cancers, he said. 

"This is a new pillar (in cancer care) that we're developing," Singh said. 

"It's going to revolutionize the way we treat cancer completely in the years to come."

RLT works by finding a target, which is usually a receptor on the surface of cancer cells that doesn't exist in healthy tissue, he said. 

Successful radioligand therapy depends on identifying that receptor in each patient's cancer cells using a PET scan, then delivering the right radioactive medication — like Pluvicto for prostate cancer and Lutathera for neuroendocrine tumours — that will bind to the cancer cells and kill them without harming healthy cells, he said.  

The Canadian Cancer Society calls radioligand therapy "a remarkable breakthrough" that started with Lutathera for neuroendocrine cancer around 2018. 

”We saw patients having metastases all over their body and then with one or two treatments completely cleared up. It's incredible,” said Stuart Edmonds, a pharmacology expert and the cancer society's executive vice-president of mission, research and advocacy. 

RLT also has "considerably lower" side-effects compared to traditional radiation because it minimizes harm to healthy cells, Edmonds said.  

Now that RLT's effectiveness in prolonging life for patients with metastatic prostate cancer who have run out of other treatment options has been proven, the cancer society is funding clinical trials across Canada looking at whether Pluvicto can be used for prostate cancer patients in much earlier stages of the disease.  

In the meantime, Edmonds said it's "tremendously important" to make Pluvicto publicly accessible for advanced prostate cancer patients. 

"I just want it to be available in Canada as soon as possible," he said. 

Global pharmaceutical company Novartis manufactures both Pluvicto and Lutathera.

Both the company and the agency in charge of negotiating drug pricing confirmed to The Canadian Press that they have not yet reached an agreement on how much Pluvicto should cost. 

The negotiations began in August of last year, but then had "an unanticipated delay," said Dominic Tan, acting CEO of the pan-Canadian Pharmaceutical Alliance in an emailed statement. 

"The pCPA always strives to complete the process as quickly as circumstances allow," Tan said. 

"However, negotiations are a two-way street, and as such we are unable to provide a precise timeline for when the process will be complete."

Novartis said it recognizes the "high unmet need" of advanced prostate cancer patients. 

"It is with these patients in mind that we continue to actively collaborate with the pCPA with the goal of achieving timely and responsible access to this therapeutic advance," Novartis Canada spokesperson Rosa D'Acunti said in an emailed statement. 

"We are hopeful that an agreement with pCPA that recognizes the significant innovation Pluvicto represents and the value it brings to patients is within reach."

This report by The Canadian Press was first published July 6, 2024. 

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.