"Last week, I learned that I have been diagnosed with metastatic prostate cancer," he wrote in a statement.
"I have begun treatment, and I am surrounded by my loving wife Margaret, our incredibly supportive family, the best medical team, and our dear friends."
Sandberg, 64, made his first major league appearances as a Phillies shortstop in the 1981 season, then spent the rest of his on-field career as a Chicago Cub.
He was briefly the manager for the Phillies' top minor-league affiliate, the Lehigh Valley IronPigs, shepherding the team to its first-ever playoff appearance in the 2011 season.
In 2012, he was made a Phillies third base coach, then became the team manager the following September. He resigned the post in June 2015.
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