Last week marked a potential turning point in cancer treatment. Pharmaceutical giants Merck and Moderna announced positive clinical trial results for a cancer vaccine that is personalized to the patient.
The vaccine was shown to significantly reduce the risk of skin cancer returning and spreading.
The challenge now is turning this promising breakthrough into an affordable, scalable treatment available to Canadian patients.
“We finally, finally, after decades, decades of trials investigating vaccines have a vaccine that has a positive result,” said Dr. Marcus Butler, a medical oncologist at The Princess Margaret Cancer Centre in Toronto.
‘Personalized medicine’
For decades, researchers have tried to harness the body’s immune system to fight cancer.
For skin cancer in particular, researchers were keen to find an alternative to chemotherapy and radiation, which have historically had poor results treating melanoma.
During the pandemic, Moderna and others developed mRNA vaccines, which give cells instructions to make a piece of the COVID-19 virus. This then helps the immune system recognize and fight the actual virus.
Jumi Shin, a chemistry professor at the University of Toronto, compares the approach taken with the COVID vaccine to the one used in the new cancer vaccine: both teach the immune system to recognize a specific target.
In the case of the melanoma vaccine, called V940, scientists sequence the DNA in a patient’s tumour to identify mutations unique to the cancer, then predict which ones the immune system can recognize.
Those targets are encoded into a personalized mRNA vaccine, developed by Moderna, which trains a patient’s immune system to recognize and attack cells carrying the mutations.
“This is truly personalized medicine,” Shin said.
A Phase 2 trial for V940 found that patients who received the vaccine alongside a Merck immunotherapy drug were 49 per cent less likely to have their cancer return or die, and 59 per cent less likely to have their cancer spread or die.
The vaccine and immunotherapy drug help “release some of the brakes” on the immune system, says Butler. This allows the cancer-fighting cells generated by the vaccine to attack tumour cells.
“It’s a one-two punch sort of phenomenon,” said Butler.
The Phase 2 trial was followed by a Phase 3 trial involving 1,137 patients. Researchers found the vaccine achieved their main goal of improving recurrence-free survival, though the full results have not yet been released.
“[From] the Phase 3 [trial] … all we know is that the study was positive, but … we don’t know what the magnitude of the difference is,” Butler said.
The vaccine also has some known limitations. It cannot currently be used to treat incurable cancer that has metastasized. It is also a challenge for scientists to predict which tumour mutations a patient’s immune system will recognize.
“It’s a bit of a hit or miss because a lot of these predictions are not perfect,” said Butler.
There is also a question about how much of the benefit comes from the cancer-specific vaccine. Some research suggests that mRNA itself can stimulate the immune system and make cancer drugs more effective, even without cancer-specific targets.
Cost burden
Moderna and Merck say they now plan to engage with regulators to seek regulatory approval for the vaccine.
If Health Canada were to approve V940 — a process that could still take years — this would be followed by a cost-effectiveness review by Canada’s Drug Agency, price negotiations and funding decisions by individual provinces, says Butler.
The vaccine’s personalized nature presents another challenge.
Unlike conventional drugs manufactured in large batches, each V940 vaccine is built using information from an individual patient’s tumour.
Shin says a bespoke vaccine can currently be produced in about six weeks after the tumour is sequenced and a target identified.
“I think they’d have to have a specific facility doing … this work,” she said.
Neither Shin nor Butler could say what V940 would cost, but both pointed to the potential cost burden of delivering a bespoke treatment to large numbers of patients.
Melanoma is the seventh most commonly diagnosed cancer in Canada. An estimated 11,300 Canadians are expected to be diagnosed with it in 2026, and about 1,250 are expected to die from it.
Butler says vaccinating every high-risk patient could put additional pressure on an already stretched health-care system. But the vaccine also has the potential to reduce overall costs if it prevents patients from needing more intensive treatment down the road.
“If we can reduce relapse and the morbidity from requiring systemic therapy … it is a big deal, especially given that the treatment is well tolerated,” said Butler.
