Last week, 10-year-old Danny Feltwell Jr pitched in his team's playoff game - but just two months prior, he was fighting for his life as the donor bone marrow that had been keeping him alive began attacking the little boy's healthy tissues.
In that short span of time, Danny's life was turned around with the help of an experimental drug to treat the post-transplant condition threatening his life - but it was hard-won, CBS 3 Philly reported.
A bone marrow transplant had saved him from non-Hodgkin lymphoma had turned against him in the rare graft vs host disease.
There is a drug approved to treat the life-threatening condition, but it is only approved to treat adults.
After a months-long battle, Danny's father, Dan, a single parent, finally won his fight with the family's insurance company and got the costly treatment covered.
Now, just two months after receiving an experimental treatment, Danny has made his return to the pitcher's mound and life as an active kid.
After a years-long battle with non-Hodgkin lymphoma, the donor bone marrow that treated Danny Feltwell Jr's (pictured) cancer attacked his body. Just two months after he started an experimental treatment, the 10-year-old is back on his feet and pitching again
Danny was diagnosed with non-Hodgkin lymphoma when he was just two years old.
The white blood cell cancer accounts for about five percent of all childhood cancers.
It has a high five-year survival rate (around 80 percent in children) but in some the cancer keeps returning.
The first round of chemotherapy kept the disease at bay for most of Danny's life, but after four healthy years, the lymphoma returned with a vengeance.
For doctors, that was the sign that chemo wasn't the best approach to rid the young sports fanatic of the disease.
So began the agonizing wait for a bone marrow donor who would be a match for Danny.
People who suffer from non-Hodgkin lymphoma produce unhealthy white blood cells that form tumors and struggle to fight infection.
The immune cells develop from stem cells, which are housed in the bone marrow.
Diagnosed with non-Hodgkin lymphoma at just two (pictured) Danny has spent much of his life sick, in chemo treatments and in and out of the hospital
The first line of treatment for Danny's disease was chemo, a brutal therapy for the little boy
So the transplant of marrow from a healthy person whose HLA proteins matched Danny's would replace his defective