Cardinal Francis George of Chicago is continuing cancer treatment and has agreed to take part in a clinical trial of a new anti-cancer drug, his archdiocese has announced.

"The cardinal is grateful to those who are praying for him and requests that everyone continue to remember him in their thoughts and prayers," the Archdiocese of Chicago said Aug. 22.

Cardinal George, 77, is taking part in a clinical research trial at University of Chicago Medicine for a new drug that may activate the cells of his immune system to attack cancer cells, the archdiocese reported. The drug has shown promise for patients with the same type of cancer as the cardinal's and the new study of the drug seeks to confirm the results.

First diagnosed with bladder cancer in 2006, the cardinal underwent a five-hour operation at age 69 to remove his bladder, prostate gland and sections of his ureters, the tubes which connect the kidneys to the bladder.

In August 2012, a medical examination of the cardinal discovered that cancerous cells had returned to his kidney and a nodule in his liver.

Cardinal George recently underwent a regular medical procedure to replace a stent in his ureter, which he has done every six months in recent years. He continues to maintain his regular schedule, the archdiocese said.

Earlier this year, the cardinal spoke of his health struggles in a column for the Catholic New World, saying cancer "will most probably eventually be the cause of my death."

Cardinal George has headed the Archdiocese of Chicago since 1997. He is the first native of Chicago to become the city's archbishop.