Nemours Children's Hospital in Lake Nona, Florida, treated the first child in the entire world using a new cancer drug that one mother says saved her daughter with zero side effects.

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Ava Jaus was only 20 months old when her mother noticed her little girl wasn’t walking well. It turned out to be a rare malignant tumor in her right leg.

“I felt like I took a deep breath in and I couldn’t breathe back out,” said Ava’s mother, Kate Jaus, who lives in Clermont.

Instead of giving Ava chemo or radiation, doctors at Nemours wanted to add Ava to a clinical study for Vitrakvi, known generically as larotrectinib.

“We realized [a change] in two days," Kate Jaus said. Her daughter’s tumor shrank by 82 percent in five months, allowing doctors to remove it without amputating Ava’s leg.

"I don't know how else to describe it, except to say I can breathe again," she said.

Vitrakvi is taken via a pill for adults or as a liquid for children who have cancer. The drug only targets a specific rare mutation found in some cancers, which is why Ava and other patients didn’t lose their hair or suffer from severe fatigue or nausea.

This week, the Food and Drug Administration granted accelerated approval for the drug, thanks in part to Ava, patients like her and their doctors here in Central Florida.

To be clear, the treatment is expensive: $11,000 a month for children, though some insurance companies will cover it.

Meanwhile, Ava is still part of the study. She'll continue to be monitored for several more years.