By Stephanie Stahl

PHILADELPHIA (CBS) – It’s a breakthrough that could help save the lives of children everywhere. An experimental drug used to treat childhood cancer is showing amazing progress. And it’s being put to use in Philadelphia.

The amazing discovery comes from The Children’s Hospital of Philadelphia. This research was initially measuring basic safety, but doctors quickly discovered it did much more. Now, it’s saving lives.

Zach Witt is a vibrant six-year-old who now has a full head of hair. Just a year ago, Zach had no hair.

“I feel great right now. And I didn’t feel so great,” said Zach.

In 2010, Zach was diagnosed with a type of anaplastic large cell lymphoma that has an abnormal gene called ALK. It makes it harder to treat.

“Right at that point in time, it’s just every parent’s nightmare,” said John Witt, Zach’s father.

Zach’s parents were even more devastated when traditional chemotherapy failed, and his cancer came back. They turned to experimental pills as a last hope. The drug was being tested on patients who don’t respond to standard treatment, and it targets and turns off the ALK gene that fuels Zach’s cancer.

“With this one drug alone, seven of the eight patients’ tumors, we can’t detect them anymore. It’s been humbling. It’s an exciting early result,” said Dr. Yael Mosse, a pediatric oncologist at The Children’s Hospital of Philadelphia and the lead researcher of the study.

She says the drug Crizotinib, already approved for adults with lung cancer, has minimal side effects in children with different kinds of cancers, including the hard to treat neuroblastoma, which is what killed Alex Scott, the little girl who started Alex’s Lemonade Stand to fight childhood cancer.

“The responses that we’re seeing in neuroblastoma are early and promising for children who historically have had no hope for any treatment that could be of benefit to them,” said Dr. Mosse.

Zach is now the face of hope for many. The medication worked for him right away. He’s currently cancer free.

“It definitely saved his life,” said Pam Witt, Zach’s mother.

“It’s one of these outcomes that you hope for, and pray for, and here it is,” said John.

The drug is only for patients who have the ALK gene abnormality. Doctors say these results are preliminary, but research is continuing at CHOP. They hope to get it to the front line of treatment as soon as possible.

For more on the CHOP study, click here.

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