"You have to confront them head on. And this is just another one," Kelly said Monday after revealing he's been diagnosed with squamous cell carcinoma.
Kelly drew upon his family, faith and perseverance when facing major hurdles. Kelly leaned on those strengths to help overcome the death of his son, Hunter, and of his mother, and whatever obstacles stood in his way on the football field.
"I'm down at the bottom. But I will rise to the top again," Kelly said. "I am extremely confident in my road to recovery. I plan to tackle this challenge head on, as we Kellys always do."
Informed of the diagnosis two weeks ago, Kelly called the prognosis for recovery "very good." He said tests show the cancer is isolated to the jaw.
Doctors plan to remove part of Kelly's jaw during an operation at a Buffalo hospital on Friday. It won't be determined until after surgery whether he will require chemotherapy
"We caught it in time," the 53-year-old Kelly said. "It's just another challenge for me and I know I'll beat it."
The announcement was made shortly before the start of the former quarterback's 27th annual Kelly for Kids charitable foundation's celebrity golf tournament.
The news of Kelly's condition immediately drew support from those attending the tournament.
"The first thought is you say a prayer that everything works out OK," said Bill Polian, former general manager of the Bills, Panthers and Colts. "Secondly, he didn't earn a reputation as the toughest guy ever to play quarterback for no reason at all. So if anybody can overcome this, Jim can. He takes challenges head on."
Receiver Andre Reed, Kelly's favourite target, called the quarterback a "tough dude."
"Jim's a fighter. We think he'll be OK. We're all in his corner," Reed said. "He's such a resilient guy, and that's been our motto forever, in whatever we did.
"He's got the support, and Jim will be OK."
Kelly spent 11 seasons with the Bills before retiring following the 1996 campaign, and has since made Buffalo his home. Known for his fearless, swashbuckling style, Kelly was the face of Bills teams that made four consecutive Super Bowl appearances in the early 1990s, only to lose them all.
Inducted into the Pro Football Hall of Fame in 2002, Kelly still holds nearly every significant career franchise passing record: 35,467 yards, 237 touchdowns and 26 300-yard games.
News of Kelly's condition also attracted many well-wishers from around the world on social media. The term, "PrayersForJK," became popular on Twitter.
"I LOVE JIM KELLY," Kelly's teammate and Hall of Fame running back Thurman Thomas posted on his Twitter account.
The diagnosis stems from pain Kelly began experiencing in his jaw in December. He initially thought it was an infection, but grew concerned when antibiotics failed to help.
Tests eventually led to doctors removing a nickel-sized cyst from his gums and nasal cavity during an operation in early March. Follow-up tests revealed the cancer.
"When you hear the word 'cancer,' it automatically scares you," he said. "But I'm very confident. My faith is definitely there. And that probably, more than anything, has kept me going, and the support I've gotten from my family."
Concerns about Kelly's health were first raised last week when his wife, Jill Kelly, posted a message published on imgur.com. Without going into detail, she noted that the family was going through a "more serious battle under our roof," and asked followers to pray for her husband "for healing."
Later, a youth sports foundation in Sioux Falls, S.D., announced that the Hall of Famer would not be able to attend the Hy-Vee/Sanford Legends banquet on June 13 for personal reasons.
This is but the latest operation Kelly will have had over the past few years. He's also had surgery to correct back, neck and hernia problems.
Kelly has remained active despite the diagnosis.
On May 26, he joined country music artist Tim McGraw on stage and threw footballs into the crowd during a concert outside Buffalo. A week earlier, he attended The Preakness in Baltimore.
And then there was Kelly playing host to the many weekend festivities involving his charitable foundation.
Kelly was upbeat in addressing reporters Sunday, while attending the foundation's annual gala and auction. He was just as engaging before the golf tournament in making sure to greet many of his guests. Taking the microphone to start the tournament, Kelly joked while reminding everyone to enjoy themselves, cautioning that mulligans were not allowed.
"Jim cuts a wide swath," former teammate turned broadcaster Steve Tasker said. "He doesn't forget people. And for that, people love him. That's why Buffalo loves him. That's why I love him.
"He's a teammate in life."
The Kelly for Kids Foundation was established in 1987, and has since donated millions of dollars to numerous organizations around the region.
Kelly later founded the Hunter's Hope Foundation in honour of his son, Hunter, who was born with Krabbe disease. That's an inherited degenerative disorder of the central and peripheral nervous systems. The disease hinders development of the myelin sheath, a fatty covering that protects the brain's nerve fibers.
Given little more than three years to live, Hunter died at the age of 8 in 2005.