WGRZ provided a statement from the 58-year-old Pro Football Hall of Fame member:
Kelly was originally diagnosed with squamous cell carcinoma, a skin cancer, in 2013. Part of his upper jaw had to be removed, and when further testing showed the cancer had spread to his sinus area, he underwent radiation and chemotherapy treatments.
Last January, he told John Wawrow of the Associated Press that the treatment had taken a toll, however, leaving him unable to produce saliva and without the sense of taste.
"I have a story to tell. I want people to understand that we're all going to go through things in our lives," Kelly told the AP about his effort to remain upbeat. "It's the attitude that you have and the people that you surround yourself with to be able to come out on top."
Earlier this year, Kelly walked his daughter Erin down the aisle at her wedding. His wife Jill posted an emotional message on Instagram before the event:
The Bills released a statement about Thursday's news:
"We are deeply saddened to hear the news about Jim Kelly and his impending battle with cancer. Jim is a tough and courageous man and we know he will fight this battle with strength and determination. The Buffalo Bills will support the Kelly family during this trying time and we ask our fans to pray for the family as Jim begins the treatment process and the road to recovery."