His best chance to beat the disease is to have a bone marrow transplant. This week his family got news there's a match.
In fact, there's more than one match — there are three.
"It's surprising. It's remarkable, I don't even know what to say," said Jean-Gilles' cousin Mona Ditcham.
Diagnosed last month
Jean-Gilles, a child entertainer best known for his recurring role in Les Gags, was diagnosed with acute myelogenous leukemia last month.
Ditcham told CBC News the diagnosis was a complete shock. She said one day, Jean-Gilles had a headache, and when he went to the doctor they discovered he had cancer.
It is one of the most common forms of leukemia in adults — the average person diagnosed with the disease is a 54-year-old male.
Since Jean-Gilles is only nine, his treatment is experimental.
His condition deteriorated so quickly that doctors told the family last week he would need to find a compatible bone marrow donor.
Jean-Gilles' mother, Marie-Josée, took to Facebook to ask for bone marrow donations. Her post was shared over 5,300 times.
“It’s only natural. You see a child that’s sick, everybody wants to help,” said Ditcham.
Well-wishers requested testing kits to see if they were compatible donors.
"We had more than 10,000 people who signed up to receive one of those swab kits," said Héma-Québec spokesman Laurent Paul Ménard.
So far, 7,000 self-testing kits have been dispatched. Héma-Québec usually sends out 1,500 a year.
While kits were being mailed, Gadoury's medical team told him they had found three matches.
The family is still encouraging everyone who got on the stem cell registry for Jean-Gilles' sake to send in their swabs for other cancer patients.
Héma-Québec says not everyone who signs the registry bothers to mail back their kits.
"We ask that they return it because it has a potential of saving a life," Ménard said.
Outpouring of support
Ditcham said the entire family has received a steady stream of support since Jean-Gilles' was admitted to hospital. Through online fundraising, they’ve received financial support for his mother.
The family also set up a postcard program for Jean-Gilles. He's receiving postcards from around the world, and marking off every new location with stickers on a map.
Ditcham said Jean-Gilles appreciates the support.
“Of course, he’s absolutely thrilled with the messages people have sent out. He’s a show-boy. He likes that kind of stuff,” she said adding that Jean-Gilles's health condition is stable.