His Brain Tumor Was a Hopeless Case. Then an Experimental Medicine Made It Melt Away.

IMMUNOTHERAPY IS CHANGING CANCER TREATMENT FOREVER.

- CHRISTOPHER COX

ON A SCREEN ON THE FAR WALL, I COULD SEE A HOLE WHERE THE TUMOR HAD BEEN, AN ALMOST PERFECTLY ROUND MINIATURE PLANET.

One morning at the end of April 2023, Marcela Maus, a cancer researcher at Mass General in Boston, got a call from her colleague Bryan Choi. “He called me, and he’s like, ‘Oh my God, oh my God, oh my God!’ And I’m like, ‘What is going on?’ ” Maus said. Choi, a neurosurgeon with the languid demeanor of a surfer, was not given to outbursts. Maus hung up the phone and hurried over to his office.

The day before, Choi and Maus had treated their first patient in a clinical trial for an aggressive brain cancer called glioblastoma, infusing genetically modified white blood cells directly into the fluid surrounding the brain. They had been up all night worrying, especially after the patient, a 74-yearold man, developed a fever. Choi had ordered an MRI. “We were not looking for the results,” he said. “We were trying to make sure that our patient was okay.”

When Maus got to Choi’s office, images from the MRI were loading on his screen. They stared in wonder: The patient’s tumor, which a few days before had shown up on the scan as a bright blob the size of a strawberry, had almost entirely disappeared. No one had heard of that kind of regression in glioblastoma, especially not overnight. “My first instinct was that there was something wrong with the MRI scanner,” Choi said. But then the follow-up scans looked even better.

Several weeks later, they treated a second patient, a civil engineer from upstate New York named Tom Fraser, and the process repeated itself: the infusion, the fever, and the rapid regression of the tumor. “It was almost like clockwork,” Maus said, still sounding astonished months later. After a third patient had a similar response, she paused the trial and wrote up her results.