Pagano has been diagnosed with acute promyelocytic leukemia, or APL- a rare form of acute myeloid leukemia- known as AML.
While doctors say there's fewer than ten-thousand cases of AML nationally each year, Dr. David Zimmerman says there are even fewer cases like Pagano's.
"I probably see one or two cases a year of his specific type of AML. I probably see a case or two a month of AML, but a specific APL-variant I see a couple a year," Zimmerman says.
Symptoms of APL include bruises, tiredness and nose and gum bleeding.
Reports say Pagano sought medical attention during the colts' bye this past week.
Doctors say he'll be hospitalized in Indianapolis for the next six weeks, undergoing aggressive chemotherapy and medication.
Treatment could last much longer.
"The treatment after that initial month of inpatient care, there's an additional treatment that goes on for four to six months, so his season is pretty much over. With this diagnosis, it's essentially impossible to function in the role he's been in," Zimmerman says.
Dr. Gary Gize agrees.
"It's going to be impossible while he's on treatment, or at least, something he can go back to. But I don't foresee him going back this football season, no," Gize says.
At a press conference today, Colts employees supported their coach.
"I feel with every fiber of my body, and I know chuck feels the same way, that he can beat this thing," Colts owner Jim Irsay says.
Doctors say that most- up to ninety percent- of APL patients recover.
They say the first six weeks of treatment are the hardest.