George was told Monday by doctors at Loyola University Medical Center that they had found cancerous cells in his right kidney, the Chicago Sun-Times reported. The archdiocese said in a statement he will begin the first of six rounds of chemotherapy Tuesday.
The cardinal had a procedure in August to remove cancerous cells from his liver. In an appearance Friday at "Noche de Gala," the annual Hispanic Ministry awards banquet, George joked with reporters about his medical problems.
"I'm hoping that if should it be chemo, and I'm not looking forward to that, I might get some hair which I haven't had for a long time," he said.
The archdiocese says the 75-year-old cardinal plans to remain at work during his treatment, although his public schedule will probably be pruned.