(CNN) -- Indianapolis Colts head coach Chuck Pagano has been diagnosed with leukemia, according to team owner Jim Irsay, and the coach's doctor describes it as a highly treatable form of the disease.
"I am very optimistic that he will beat this thing," Irsay said during a news conference Monday. Offensive coordinator Bruce Arians will take the team's helm during Pagano's absence, the owner said.
According to the National Cancer Institute, acute promyelocytic leukemia -- the type with which Pagano was diagnosed -- is an "aggressive (fast-growing) type of acute myeloid leukemia in which there are too many immature blood-forming cells in the blood and bone marrow."
For patients who are promptly diagnosed with APL, the "disease-free survival" rate can be as high as 90% if the patient undergoes certain treatment regimens, the institute says.
Dr. Larry Cripe is overseeing Pagano's treatment. He said he doesn't know when Pagano will be able to return to football-related activities.
"The goal is to cure the disease," said Cripe. "A cure is usually defined when the cancer is in remission for three to five years."
Arians is a cancer survivor himself. He was emotional at the press conference, but kept his composure and tried to rally the Colts players.
"We have to move on from today. We are going to get ready for the Packers on Sunday," said Arians. "This football team will survive."
According to Irsay, "the coach was feeling fatigue over the last few weeks." He said Pagano had also "noticed some bruising on his body" that he thought had resulted from playing with his grandkids or perhaps some contact during football practice.
Pagano's wife urged him to see a doctor when the bruising became more prominent, Irsay said.
This is the first season for Pagano as Indianapolis head coach, and his record is 1-2 in his first three games. Prior to this season, Pagano was defensive coordinator for the Baltimore Ravens. Under Pagano, the Ravens had one of the top-ranked defenses in the league last season. Pagano turns 52 on Tuesday.
Though Irsay said it's unlikely Pagano will be "all in as a head coach this season," he said Pagano has already set a tone for coaches and players during his short tenure. Irsay said the team's primary objective now is to get Sunday's game ball after the Green Bay Packers matchup "and walk that into the hospital and put that in his hands."