Isaac Harrison is a fighter.

One month after being given 10-times the amount of chemotherapy he should have received, Isaac — who celebrates his first birthday this month — is surviving, but no one knows what the future looks like for this Philly boy.

"Sometimes he's doing good, sometimes he's doing bad," his father Kwamame Harrison said as he held his wife's hand and tried to hold it together emotionally. "He can't tell us when he's going through pain. All he can do is cry."

While Isaac was being treated for a rare and aggressive childhood cancer at St. Christopher's Hospital for Children, someone made a mistake and he was given 30 milligrams of chemotherapy medication instead of 3.3 mg. That overdosing continued for five days before a member of the medical team caught the "typographic error," according to hospital documents.

"We are simply interested in trying to understand how this could have happened and really to prevent it from happening to any other young patients in the future," said Matthew Colavita, the family's attorney.

Isaac's father said he understands mistakes happen, but he doesn't understand how it happened more than once.

"It's kind of scary to think that kind of error can happen in a hospital, just from a decimal point," said Harrison.

When doctors broke the overdose news to Isaac’s parents, they apologized and warned “this error could have severe, life threatening…lethal consequences,” according to hospital records. Doctors at St. Christopher's also arranged for Isaac’s transfer to the Children’s Hospital of Philadelphia, where he’s currently undergoing treatment and surgery to remove part of the tumor. A spokeswoman for St. Christopher's said last month the hospital could not respond to specific concerns, citing privacy laws. "It remains the focus of St. Christopher's Hospital for Chldren to provide high-quality care to every patient we serve," Kelsey Jacobsen said.

Though Isaac's condition is improving overall, he remains critical and the days are tenuous, Colavita said. "We don't know the extent of the effects of the overdose."

Isaac is the youngest of five children, all under the age of 10. Family friends have set up a gofundme page to help his parents cover medical costs as well as day-to-day expenses.