New Cancer Drug Could Cure John McCain's Glioblastoma Using a Virus

McCain Brain Tumor Scar
Senator John McCain holds a news conference at the U.S. Capitol on July 27. Chip Somodevilla/Getty Images

Glioblastoma is a rare and terrible disease. And whether or not you've been affected by a diagnosis directly, this particular kind of brain tumor has had a profound effect on every single American's life.

"This is a disease that has fundamentally changed the political trajectory of the United States," Dr. Clark Chen told Newsweek. Chen is a neurosurgeon at the University of Minnesota. Ted Kennedy and former Vice President Joe Biden's son, Beau Biden, both died from glioblastomas. Biden's death was widely cited as a reason his father didn't run for president in 2016. "Do we have President Trump today if this death had not happened?" Chen speculated.

This summer, Senator John McCain announced that he too had been diagnosed with glioblastoma this summer.

But Chen is running a part of a clinical trial for a new treatment for this kind of cancer, which has just announced a promising set of results at a conference on Friday. The treatment is being developed by Tocagen.

Beau and Joe Biden
Democratic vice presidential nominee Joe Biden and his son, Beau, in 2008. Ellen DeGeneres has jokingly suggested she would be Joe Biden’s running mate if he agrees to run for president in 2020. Paul J. Richards/AFP/Getty Images

Cancer cells excel at replicating and spreading, and glioblastomas are no exception. These brain tumors rarely stay in neat, easy-to-remove shapes. Instead, they extend microscopic threads of tumor deep into healthy brain tissue, where brain surgeons dare not cut at the risk of doing more harm than good. If the tumor comes back after an initial treatment, the survival rates are grim. Half of all patients with recurrent high-grade gliomas will die within nine months.

However, all that growth comes with a price. Cancer cells don't have the same defenses against viruses that normal cells have in their surroundings, often called a microenvironment. That leaves them open to an attack from a virus, like the one used for this treatment.

What that virus does is force cells to produce a protein called cytosine deaminase. That protein can transform an antifungal drug into a potent cancer medication. Since the virus is only able to infect cancer cells, this transformation should only happen in brain cancer cells, killing them.

When the treatment works, it works well. In one group of 23 patients, more than half of the patients survived more than a year after they got the treatment. One has survived for more than four years after being treated.

But the results from the company's most recent study in human patients come with some serious caveats. First, this is not a cure. People survived longer, but most did die. "It is irresponsible to say it's a cure," Chen said. "We think studies like this should allow some families to have a sense of hope."

Statement regarding my father @SenJohnMcCain:

— Meghan McCain (@MeghanMcCain) July 20, 2017

Second, the most promising results came from a subgroup analysis. This matters because those kinds of subgroup analyses are far less statistically powerful than the analysis of the entire study, especially when the study wasn't designed to look at this group in the first place. Third, even in that subgroup analysis, half of the patients did not respond.

Finally, this study is very preliminary. Clinical trials go through at least two or three phases. This data came from a phase-one study.

The company announced on Thursday that it would be doing one more "pivotal" study, likely the last it will run before it brings its data to the FDA for approval. That study will run into 2019.

For this investigation, the company will be restricting the experimental treatment to patients who have tumors that can be taken out, in part, during a surgery, and those who have only failed one or two other kinds of treatment. This group had the best results in the previous study.

In the future, perhaps, the therapy could be expanded to others, changing history just as much as the disease it targets.