"First round of chemo. DONE," Jill Kelly tweeted Tuesday night.
The tweet followed an earlier photo on Instagram of Kelly's first chemo treatment from his New York City hospital room.
"There's been such a big outpouring of prayers -- which I definitely need," Kelly said on Friday before his treatment began. "It makes me feel good that so many people are praying for me."
Kelly has revealed that he will have two more rounds of chemotherapy in the next six weeks, and he will also have daily radiation treatments.
Kelly's doctor has described his cancer as "very treatable and potentially curable."
A hospital statement last week said Kelly will be receiving a single dose of chemotherapy at Lenox Hill Hospital, along with concurrent daily radiation therapy treatments. The chemotherapy will be repeated as an outpatient in approximately three weeks and six weeks. The radiation therapy will be a six-week regimen carried out at the North Shore-LIJ Cancer Institute's Center for Advanced Medicine in Lake Success, N.Y.
Kelly, 54, entered the Pro Football Hall of Fame in 2001 after playing from the Bills from 1986 to 1996. He holds most of the franchise passing records.